After further experiments with the BIOS settings, the hanging occurs when the External Cache is enable. Could my CPU be on the fritz?

First thing I'd do would be to remove it from the case and try it again on the cardboard.
My 4DPS is very sensitive to being moved, the RAM simms are not very well secured, so check that as well. Also recheck the jumpers again just to be sure, perhaps someone else with idle hands moved one or more or them? I can confirm my 4DPS does ID as DX/2 as that and not as a P24D-S, so something is amiss there.

Best,
Chris

Thank you for your reply. With External Cache disabled, I am able to get to the DISK BOOT FAILURE notification, so I am going to connect my drives and test further. I didn't have to disable external cache prior, so I am wondering if my CPU is now having issues.

Now I am getting an I/O error when trying to boot from the floppy drive so that I can set things up... the gods must be toying with me.

Reseat your cpu and your ram, if that doesn't help try another cpu.
Some 486 boards reseating the bios rom helps great too, a little bit of corrosion sometime builds up on the legs which gets scraped off while reseating.

I will try that tomorrow. However, I am thinking I am either cursed or this board is having issues. Regardless of the floppy drive I am using, this board will not recognize or boot from a Win98 boot disk, or gives me an I/O error. When I try to boot from an MS-DOS 6.22 setup disk (two different disks during testing,) it hangs at "Starting MS-DOS." I have even tried a USB Floppy emulator. The Compact Flash has system files on it and will not boot, though the bios recognizes them as SanDisks hard drives.

I am not sure what is going on with this board. It will not boot from floppies, or the CF-IDE adapter. If I use a floppy emulator with a dos boot disk, or an actual floppy drive with a dos boot disk, I get "Starting MS-DOS," but it just hangs there; the system isn't locked up as I can hit capslock on and off and ctrl-alt-del to reboot. I am still getting the I/O error with a Win98 SE boot disk. If I try booting from the CF-IDE, I get "Invalid system disk Replace the disk, and then press any key.". Nothing seems to work.

This crap sadly happens too often to 386/486 boards that have seen some use especially when they have sat for weeks/months/even years without being powered up and it really sucks because usually something ends up being replaced. Reseat and check everything then try again, if all fails power the board up and let it sit for a while then power cycle it once or twice. Caps can do strange things too :s

I grabbed another RAM module and a couple 486 CPUs to test when I reset everything. I know that the CF-IDE is good, as it boots up in another machine. Do these boards have any issues with FAT32 drives? I have MS-DOS 7.10 on there, and the CF is formatted with FAT32. Though it is still strange to be having both floppy and IDE issues. The only other option after reseating everything is to get my hands on a PCI IDE controller card (which I currently do not have,) and seeing if that allows me to put this thing up.

Ok, so I swapped out the 486DX2 with another one. During boot, the board recognizes the CPU as 80486DX2-S at 66Mhz, rather than a P24D-S. It also successfully boots to my multi-config.sys, so I am diagnosing the problem as a CPU issue with the original CPU. Now to put a fan on the replacement CPU, test the floppy, and install my cards and hope for the best.

Of course, I have run into more issues. CTMouse doesn't detect the mouse (I have a ps2 bracket adapter connected to the mouse port on the motherboard.) Also, when I connect a cdrom to the secondary IDE port, it cancels out the Primary port. Argh...

It might help if You could post some decent photos of Your board, etc. What brand dx2-66 are You using?
I have no idea what your skillset is but a common error is to connect the floppy drive cable backwards on the drive, it should be opposite to cdrom/hdd.

If the mouse adaptor is a simple Serial to ps/2 adaptor it likely won't work, get a proper serial mouse if you can.

http://www.elhvb.com/webhq/manuals/486pci/tomato.zip

I build computers of various sorts. I have three retro hobby computers I have been working on. The last 486 was perfect until the board died; it had PCI slots and PS2 ports for keyboard and mouse. Some of this is new, such as the CF-IDE adapter, etc.

I uploaded a pic of the mouse connector. I was limited to what I could upload. Maybe it is wired differently than the five pin layout on the 4dps. I solved the 2nd IDE port issue and have a slot load drive running on it, and i solved the floppy issue. They were related to the faulty CPU, which now has a replacement Intel 486DX2 - 66 installed. The only remaining issue seems to be the mouse connector not being seen by the driver, though it does power the optical mouse when connected.

In addition to the mouse connector issue, I tried to flash the bios to 1.72. I followed the instructions, but I get an "erase chip fail" error and the bios will not flash. It is currently version 1.5. I cannot believe the string of issues i am having. All have been fixed except for the mouse and now the bios.

The bios chip is probably a non eraseable 27c1024. If it has a window underneath the sticker then it's eraseable via a UV light box.
You may have to get a proper eeprom of the correct size, likely like this

http://www.ebay.com.au/itm/1PCS-Flash-Memory- … xUAAOSwo6lWKkF-

Thank you much, for your reply. I will look into the bios chip issue. Do you have any information on the mouse issue? I am still thinking that my connector's wire layout differs from the mouse pin layout. I have the one 5 pin, single row connector, and a 2-row connector which will not fit, but has a different wire scheme, so I think that it isnt standard, and net searches are not providing much inn the way of PS2 connectivity on this particular board. I have a ps2/serial adapter here somewhere, and a usb-to-serial adapter, but I am reading that the power carried by the serial ports may not support an optical mouse, so I am searching for an answer to that issue, whether a proper motherboard connector, or some kind of dos-friendly PCI PS2 card.

I do not have Your motherboard, so cannot really help much as far as the ps/s pinout is concerned.
If You have a multimeter then you could easily figure out what pins are ground and +5v then the rest couldn't be too much mucking about to figure out.
Other than that hopefully someone else here can help that has that motherboard.

I am going to mess with pins and wires soon. First, I am going to test with another mouse or two. This optical mouse lights up when I use the PS2 port, though without being detected by CTMOUSE. I just connected it to the COM1 serial port with an adapter. The mouse remains unlit until CTMOUSE loads, and then it lights up, but still has no movement. Mouse was tested to be working on an Athlon XP system.

No mice work with 2 different ps/2 to serial adapters. A serial track ball works. On my ps2 connector, I swapped the yellow and blue wires, and CTMOUSE still doesn't see a ps2 mouse.