ATA100 hard drive not recognized when PS/2 mouse is not attached

I have a 3 or 4 year old PC, home-built. Windows 98se, AMD 1.3 ghz, 3
hard drives (10g AT66, 180g ATA100 and 250g ATA133). The large hard
drives are attached to a Promise Ultra card. ECS motherboard.

For quite a while (and since reinstalling all peripherals, OS, etc)
I've had a mysterious problem -- when there is no mouse attached to
the PS/2 port, the system (and Promise bootup sequence) does not
recognize the 180g hard drive, which is configured as the primary
drive on the Promise ATA100 card. The 10g hard drive is the primary
boot drive I usually use.

With no mouse attached, the system freezes when the Promise bootup
sequence tries to find the 180g drive which is configured as the
primary drive on the first ATA100 channel. After attaching a PS/2
mouse, the PC boots fine. Has anybody ever experienced this or knows
what causes this?

TODAY I have a much bigger problem, which is related -- something
seems to have gone wrong with my PS/2 port. None of my PS/2 mice work
in the PS/2 port, and so the 180g hard drive is not recognized at all.
(The PS/2 port has had a rather insecure connection to the USB/PS2
adapter hooked to the mouse.) The system will boot normally -- but
only sees the 10g and 250 hard drives. I have a boot drive /
partitioning program active "BOOT IT" (similar to "Partition Magic"),
and this program also now does not see the 180g hard drive.

Attaching a USB mouse to a USB port gives me a working mouse, but
still no 180g hard drive is recognized.

Any helpful advice is appreciated.