Pressing any Key on Keyboard causes computer to reboot

I have Windows XP SP3, 2gig of RAM
I do not know what caused this....but suddenly, when I tried to use my keyboard and key, as soon as I pressed any key...the computer would automatically reboot.

I can sucessfully do anything with the mouse actions and all seems to work fine.

I installed a program called comcast GUARD. After I rebooted my system ....I had the problem I described above.

I uninstalled the GUARD program .....still did NOT resolve the keyboard keying problem.
I did a RESTORE function to an earlier time when I knew all was working correctly. The RESTORE did not help resolve the keyboard keying that causes a REBOOT. Is there something else that I can try to correct this problem.

I have a program called REIMAGE. I ran that program....and still the keyboard problem of pressing any key, causes my computer to reboot.

I have also used a new Keyboard....and that does not help resolve the problem.

This computer worked very well about 1 hour before I installed the SAFE GUARD program.

Is there anything else i could try to help resolve the problem of "when I press any key on the keyboard, the computer automatically reboots"