My New Nightmare

I shoulda just bought a new computer.  We're coming up on a month now since my hard-drive packed it in and I decided to go all-out on the new HD, monitor, printer, and DVD-burner.  This is the longest my computer's been running in 3 weeks.  And we're coming up on 9 minutes.
I've had a very, very (VERY) good friend trying to fix this nightmare machine and he originally surmised the video card had failed.  So, out to the store and $130 later I have a new video card.  I installed it, but all I got was 'no signal' from my monitor so out it came again until my friend can look it over.  The next thing to go was the RAM. 512MB gone in an instant, so back out to the store and $160 later, I have new memory.
and computer is running --sort of.
My friend installed WinXP and OfficeXP for me, then he let it run for the afternoon with no problems.  I installed Mozilla Firefox, Norton Antivirus, and Novell Groupwise email server (work email) and...
KABLOOEY!  The computer would restart whenever I double-clicked on anything.  So, I've uninstalled Firefox, uninstalled Novell and we're at 12 minutes without a restart.
Yay.
For those keeping score, this has cost me nearly $1200.00 now.
I shoulda just bought a new computer.