Missing desktop icons and task manager

Hi there, I'm having a bit of a problem with my PC and would appreciate some advice. I have an Advent T9202 3.4G P4(hyperthreading) with an 80 Gig HD and1 Gig Ram. I am running Windows XP Pro (sp2).
Yesterday I installed "The Ultimate Troubleshooter" and used it to change some settings and turn off some start up services etc. When I rebooted my computer today the following happens:
There are no POST screens, I can't start in Safe Mode, I can't access the BIOS. The computer eventually displays the blank desktop and "show desktop" is ticked. CTRL+ESC doesn't do anything either.
I can't boot from the Windows CD or Hirens Boot disc as I can't access the BIOS to change the boot sequence. I have tried some other hard drives but get nothing. I have even tried a new SATA drive-still nothing! Somebody suggested I reset the BIOS by removing the battery, which I did. It made no difference. CTRL+ALT+DEL doesn't do anything. The only thing I can do is right click on the desktop.
I am all out of ideas, can you help?
Thanks
Dave

ps. If I remove the Hard drive and put it into a USB external drive bay and connect it to my laptop would I be able to fix the poblem from there?

Please help!!!!!!!!!

From Windows (or the blank desktop) hit the power reset button on the case and see if it restarts into the BIOS POST.

If not press Delete (or your setup key) repeatedly upon power on (in the dark).

Hi all, thanks for your help with my problem. I have finaly managed to sort it. I changed the graphics card and everything came back! Ubelievable! I was running a Matrox G2 Quad card, when I put the original NVidia back in everything reapeared.
Computers...go figure!!!!!
Thanks again
Crewey

Thanks for the update. Glad all is well.

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