Hi.

The last time I started my desktop computer (Win XP), I got a blank screen, not even the initial bios screen.  The mouse and keyboard don't work either (i.e., the lights on the keyboard and the OPTICAL mouse don't come on)

 Please note the following:
-I confirmed the monitor, keyboard and mouse work by attaching to another computer.
-I opened the chassis and ensured that there aren't any loose cards (memory, graphics), or cables (power cables, drive cables, etc.).
-I tried booting from the Win XP installation disk, but that did not work either (did not get the initial bios screen).
- I had not installed any new software, made any configuration changes or made any BIOS changes prior to this problem.

I'm inclined to BELIEVE it is a BIOS issue (b/c no initial bios screen) and not solely a hard drive issue (b/c did not boot from install disk) or solely a graphics card issue (b/c keyboard lights (e.g., caps lock) and optical mouse light do not turn on)

Any help will be appreciated!!Power supply?The fan in the chassis runs and the chassis lights come on.  Would it still be a power supply issue?  How does one test the power supply?

Thanks for your help.The best way is to borrow a known good one of the same or greater wattage and SWAP it into your machine...
PSU testers aren't all that reliable.As patio SAID, and to answer your question:
Quote

The fan in the chassis runs and the chassis lights come on.  Would it still be a power supply issue?

The best way is to borrow a known good one of the same or greater wattage and swap it into your machine...
PSU testers aren't all that reliable.