Monitor won't turn on

Having a doozy of a problem with my Mom's computer today.  It's a Dimension 4300s with Windows XP.

Started with keyboard problems.  All of a sudden, it started typing in gibberish.  Multiple characters for every keystroke.  Was fine in the morning and then all of a sudden, not so fine.  Tried the Troubleshooter, which indicated I should uninstall the driver, reboot and let the computer reinstall the driver.  Honestly, it sounded simple enough.  Upon reboot, when I plugged the keyboard back in, I got an error (blue screen) that indicated there was a driver stuck in a "loop" and it said the problem was with: 16MB ATI Rate 128 Ultra (monitor) driver.  So I used the Windows Update to see if they had an updated driver.  They didn't but she had some Critical Updates due, so I installed those and it was upon reboot after that that the problems multiplied (yes, I should have left well enough alone, I know).

Mouse was frozen.  So no keyboard and no mouse.  Trying to plug in the keyboard got me another blue screen error.  She does have all her original CDs with drivers, etc but with no mouse and no keyboard, I can't use them.  So I tried shutting it down and restarting, to see if I could get the mouse back (it had been working fine earlier) and now the monitor light turns green initially when the power strip goes on, but then turns itself off (yellow light).  The only thing I can think of right now is it might be her video card?  I'm willing to replace it if that's the case.  But if there's any other suggestions, I'd try just about anything right now.  Many thanks for any ideas.