This is an Acer dekstop Athlon 64 2 GB RAM with a year-old installation of XP pro sp3 on one partition, and a 6-month-old up-to-date Vista Home Premium on the next. The dual boot has been working fine until today.

But suddenly, the PS2 keyboard will not move the curser in order to select the OS. I find that the keyboard will also not work to enter the BIOS setup or RAID utility, or to boot from a CD. There seems to be no keyboard at all at startup.

It WAS attached to a Linxcell KVM swtich which has been working fine for 3 years. But when I removed the KVM swtich and plugged the PS2 keyboard and mouse dierctly into the PC, still no keyboard function at startup - even after swapping out keyboards. (I don't have a USB keyboard to try)

I obviously cannot therefore select Vista as the OS to run, since the default was set to XP Pro. And my system startup does not even show Vista as an option - (I hestitate to edit boot.ini manually to include Vista, since it warns me that Vista uses BCDedit. In fact, in view of the fact that my new OS selection screen refers to XP as a "Previous Version of Windows", this leads me to believe that perhaps Vista is controlling the dual boot, and not XP. I just found out that's true... )

However - oddly enough - once XP is booted up, the keyboard and mouse work just fine. So it can't be a problem with the keyboard controller.

I'm a beginner tech, and this is quite confusing to me.
Thank you anyone!

Oops...I just removed the CMOS battery for a few minutes, and the keyboard came back. Had to reset the time and load optimized defaults, etc. But it's working again.