Reply 20 of 23, by ArcadEd

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You can use ChkDsk to see if you have boot virus. Here is some info

"Boot-sector viruses are spread to computer systems by booting, or attempting to boot, from an infected floppy disk. Even if the disk does not contain the MS-DOS system files needed to successfully boot, an attempt to boot from an infected disk will load the virus into memory. The virus hooks itself into memory as if it were a device driver. The virus moves the Interrupt 12 return, allowing it to remain in memory even after a warm boot. The virus will then infect the first hard disk in the system. Because the virus moves the Interrupt 12 return, the MS-DOS system memory will be 2K (2048 bytes) smaller than normal. This can be verified by running the MS-DOS CHKDSK command.

For example, if your system has 640K, CHKDSK will report: 655,360 Total Bytes Memory

If the system is infected with a boot-sector virus, CHKDSK will report: 653,312 Total Bytes Memory (this value might be different depending on the virus, but anything other than 655,360 usual indicates boot sector virus)

Once a system is infected with a boot-sector virus, any non-write-protected disk accessed by this
system will become infected. For example, simply doing a DIR command on a floppy disk will cause the disk to become infected with the virus."

Seeing as you already tried Fdisk /mbr
There used to be this old antivirus boot disk we would use to fix it. I wanna say it was even a microsoft antivirus for dos but it was so long ago I can't remember.
If chkdsk reveals a virus, maybe any anitvirus that has a boot disk can find it.

Update: I found what we used to use, it was made my Microsoft.

Reply 21 of 23, by Jo22

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"People often recommend the undocumented DOS command FDISK /MBR to solve problems with the MBR.
This command however does not rewrite the entire MBR - it just rewrites the boot code,
the first 446 bytes of the MBR, but leaves the 64-byte partition information alone.
Thus, it won't help when the partition table has problems."

Source: https://www.win.tue.nl/~aeb/partitions/partit … es-2.html#ss2.7

"FDISK /MBR (for all of you who wanted to know!)

No matter what version of FDISK you have (from MS-DOS 5.0 or higher that is), you can always enter the command:
FDISK /? at a DOS prompt, and your Windows machine should respond with:

Configures a hard disk for use with MS-DOS. [ Ah! And Windows too! ]


/STATUS Displays partition information. [ A nice safe switch. ]
/X Ignores extended disk-access support. Use this switch if you
receive disk access or stack overflow messages.

So, where's the /MBR switch? Well, that's the reason it's often called an undocumented switch! It's never displayed here; neither are any of the many others...
But these various switches are documented in a number of Microsoft books and web pages... Especially in their Knowledge Base articles
see for example: FDISK /MBR Rewrites the Master Boot Record (Q69013) (which has a nice summary of what this switch does).

Basically, it will overwrite everything that's not part of the 64-byte Partition Table near the end of Absolute Sector 0 (the very first physical sector on a hard disk). But read on...

Over and over again you'll read or hear that FDISK /MBR destroys the Partition Table too! For example, here's a quote from another KB article:

" WARNING: This process will repair the bootstrap code and the 55AA signature by rewriting sector zero, but it will also overwrite the partition table entries with all zeros,
rendering your logical drives useless (unless, that is, the 55AA signature is manually entered using a disk editor prior to performing an FDISK /MBR). "

First, reading the quote in context, shows that this applies only if the Signature ID Word AA55h (or 55 AA as seen in a disk editor) has been corrupted!
But beyond that, I can state that after having made several tests using the newer FDISK programs from Windows 95B, 98, 98SE and ME,
that none of the FAT32 capable FDISK programs will ever zero-out Partition Table data; even if the Signature Word AA55h has been erased!
{You should, of course, test that out yourself and always make a backup copy of your Partition Table.}

However, it's also a proven fact that previous versions of FDISK (such as MS-DOS 6.22), will wipe out the Partition Table data with zero bytes under the same circumstances!
So, it appears that Microsoft and others would rather err on the side of caution instead of telling customers it's OK to use the FDISK from,
say a Win 98 boot disk, without worrying about losing their Partition Table data (if it's used correctly).

CAUTION: After stating all of the above, you still need to understand that FDISK /MBR may seldom be a cure for your own MBR problems! Why?
Because it's almost always the Partition Table data itself that has been changed (such as the indicator showing which partition is Active; i.e., bootable).

And if some type of multi-boot manager (which very often resides on more than just the first sector) should fail, FDISK /MBR might not help at all;
UNLESS you kept a record of all the Partition Table data, and are capable of entering that data back into a Table of ALL zeros.
Fortunately, there are some nice tools available (see below) to do that."

Source: https://thestarman.pcministry.com/asm/mbr/FDISK.htm

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 23 of 23, by Caluser2000

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zapbuzz wrote on 2021-07-20, 18:05:

what i'd like to know is, did anyone actually help or not 🤣

Of course you did. Along with a bit of entertainment for the rest of us....😉

There's a glitch in the matrix.
A founding member of the 286 appreciation society.
Apparently 32-bit is dead and nobody likes P4s.
Of course, as always, I'm open to correction...😉