If your running Windows 2000, 2003 Server or XP, and have this problem, I just found a possible answer (it worked for me).
I posted it in the "tips" section of the forum.
If you once had UDMA on your IDE channels, ATA/ATAPI devices, and are using power-savings on your system, your device modes may now be at PIO.
After a while, the OSes can't figure out what's going on as the system goes in/out of "suspend" and they start dropping the modes down, until your are finally at PIO 0.
Check it out.
Bob T.

I posted it in the "tips" section of the forum.
If you once had UDMA on your IDE channels, ATA/ATAPI devices, and are using power-savings on your system, your device modes may now be at PIO.
After a while, the OSes can't figure out what's going on as the system goes in/out of "suspend" and they start dropping the modes down, until your are finally at PIO 0.
Check it out.
Bob T.