I have to wonder if 486 pinout differences are causing an NMI on your system somehow.
It's unlikely that a board with 72 pin SIMMs would ship with DRAM parity enabled, unless you turned it on. And that error looks more like ISA slot parity check anyway since there is no address given.
I would double check that you are using the Cyrix M7 settings, including the resistor packs--Cyrix 486 CPUs are the odd ones.

Try to disable power management stuff in the setup. I suppose jakethompson1 might be on the right track that CPU jumpering is incorrect, but this can be mitigated by not using power management.

Some processors have a special system management mode, that can be entered using a special "system management interrupt". The handler for the system management interrupt might then decide to reduce the processor clock speed (if supported by that board), or enable some throttling mechanism in the chipset. Other 486 processors do not have a system management mode, so the power management code is not executed by invoking a system management interrupt, but by invoking the non-maskable interrupt that also is used for parity error reporting. Your processor does support system management mode, and the BIOS might install power management code for the system management mode. On the other hand, there are jumpers on the mainboard that route the signal from the chipset that some idle timer expired either to the system management mode interrupt pin (for processors with system mamangement mode) or to the NMI pin (for processors without system management mode). If you have the jumper set to route to NMI, the power management interrupt generated by the chipset will generate an unexpected NMI instead of the system management interrupt.

jakethompson1 wrote on 2025-10-22, 16:54:

I have to wonder if 486 pinout differences are causing an NMI on your system somehow.
It's unlikely that a board with 72 pin SIMMs would ship with DRAM parity enabled, unless you turned it on. And that error looks more like ISA slot parity check anyway since there is no address given.
I would double check that you are using the Cyrix M7 settings, including the resistor packs--Cyrix 486 CPUs are the odd ones.

I checked the m7 cyrix jumpers on the motherboard and they qll seem to be set up correctly
https://imgur.com/a/CIR6jg4

mkarcher wrote on 2025-10-22, 19:18:

Try to disable power management stuff in the setup. I suppose jakethompson1 might be on the right track that CPU jumpering is incorrect, but this can be mitigated by not using power management.

Some processors have a special system management mode, that can be entered using a special "system management interrupt". The handler for the system management interrupt might then decide to reduce the processor clock speed (if supported by that board), or enable some throttling mechanism in the chipset. Other 486 processors do not have a system management mode, so the power management code is not executed by invoking a system management interrupt, but by invoking the non-maskable interrupt that also is used for parity error reporting. Your processor does support system management mode, and the BIOS might install power management code for the system management mode. On the other hand, there are jumpers on the mainboard that route the signal from the chipset that some idle timer expired either to the system management mode interrupt pin (for processors with system mamangement mode) or to the NMI pin (for processors without system management mode). If you have the jumper set to route to NMI, the power management interrupt generated by the chipset will generate an unexpected NMI instead of the system management interrupt.

Alright, honestly, never heard about these power mamagment stuff before so this could be the issue

I found this in the bios setup:
https://imgur.com/a/QA75G4U
So now Ill disable it as you said and see if it changes anything

nimakata wrote on 2025-10-22, 21:21:

Alright, honestly, never heard about these power mamagment stuff before so this could be the issue […]
Show full quote

mkarcher wrote on 2025-10-22, 19:18:

Try to disable power management stuff in the setup. I suppose jakethompson1 might be on the right track that CPU jumpering is incorrect, but this can be mitigated by not using power management.

Some processors have a special system management mode, that can be entered using a special "system management interrupt". The handler for the system management interrupt might then decide to reduce the processor clock speed (if supported by that board), or enable some throttling mechanism in the chipset. Other 486 processors do not have a system management mode, so the power management code is not executed by invoking a system management interrupt, but by invoking the non-maskable interrupt that also is used for parity error reporting. Your processor does support system management mode, and the BIOS might install power management code for the system management mode. On the other hand, there are jumpers on the mainboard that route the signal from the chipset that some idle timer expired either to the system management mode interrupt pin (for processors with system mamangement mode) or to the NMI pin (for processors without system management mode). If you have the jumper set to route to NMI, the power management interrupt generated by the chipset will generate an unexpected NMI instead of the system management interrupt.

Alright, honestly, never heard about these power mamagment stuff before so this could be the issue

I found this in the bios setup:
https://imgur.com/a/QA75G4U
So now Ill disable it as you said and see if it changes anything

So, disabling this didnt help, still getting the "parity check" error

Does the RAM have parity chips? Do you have pictures of the RAM sticks?

Some motherboards force NMI on and the RAM needs to support it. (My AcerPower 386/33W)

MikeSG wrote on 2025-10-23, 11:39:

Does the RAM have parity chips? Do you have pictures of the RAM sticks?

Some motherboards force NMI on and the RAM needs to support it. (My AcerPower 386/33W)

Yes, here you go:
Old ones: (2x4mb)
https://imgur.com/a/KSaw9bI

New ones: (2x8mb)
https://imgur.com/a/87nLIpT

So, today ive changed cyrix to intel dx2-66 and still same error shows up
Ofcourse i set up jumpers once again for new cpu so everything should be fine
Any ideas what could be the problem?

Is the parity error only in windows, or in Dos as well when you don't touch the keyboard for a long time?

Are you running fast RAM settings or normal?

Does your motherboard have cache? Have you tried reseating the cache chips?

Are you using any DMA supported cards? Such as SCSI controller.

Have you tried taking all ISA/PCI cards out of the system except for the video card and seeing if the error returns? Changing the video card?

Hard to know what the problem is when it only says "parity error" and the RAM is fine... Ruling things out is what I would do next...

Sorry for not thinking about it earlier. Most likely, your issue is a software problem: Your system seems to be infected by the "Parity Boot" virus. This virus is too stupid to protect itself from being overwritten, so just run "FDISK /MBR" when booted into DOS, and then press the reset button or power cycle the system. Do not use Ctrl-Alt-Del! Get a DOS virus scanner (any virus scanner from 1994 or newer will do) and scan all your floppies. Any good virus scanner will not just detect the virus, but also be able to completely remove it without any residue.

this is indeed a Parity boot sector virus. use my antivirus tool to remove this virus, no need to boot from a clean floppy just extract and copy the tool to a floppy disk or hdd then run it from there. it will disable the virus even if it's active in memory. remember to take a screenshot / photo of every step as you go along the process of disinfection.. good luck

Thank you two so much, I would never think that there was a virus like that, makes sense now because when I bought the hard drive there was already ms dos installed and I decided not to change it since there was nothing but some drivers, but most likely it also has that virus which almost made me go insane after I tested all the things that could be broken and nothing changed, anyways once again thank you guys, I think we can say that problem is solved.

Problem will be solved when the virus is removed 😀. but you can't just use "FDISK /MBR" command if you boot from the hard disk since this virus will be active .this virus is stealthy and won't allow you to write to the MBR.. use my portable antivirus since it fits in a floppy disk and also do scan all you floppy disk after disinfecting the hard disk