PC running badly after s/w install

Gigabyte GA-7ZM, Duron 800,
512Mb PC133(2x256), Seagate 40Gb 5400rpm H/D,
Elsa Gladiac MX 32Mb nVidia GeForce2,
Genius 128Value sound card,
Diamond SupraExpress 56i Pro V CC V.90.

I recently bought the hard drive, seemed to run well after complete install, games, interrnet, no probs.

Installed new CAD system (30 day trial), noticed graphics "jumping" when playing games thereafter (could have been doing it before, but I am sure I would have noticed).

While playing driving games, the screen will "jump" to a later frame on a regular basis, it is worse if it is more graphically intense, as if the whole computer has been slowed down. Pages on the internet take longer to load up, and the gifs & jpegs on the screen will slow down the scroll feature very noticably.
IT WAS NOT LIKE THIS BEFORE THE CAD INSTALLATION.

Still the same after uninstallation of said CAD s/w.
Reinstalled games, drivers (all) etc., still the same.
Formatted h/d, complete new install (without CAD s/w), still the same.
Flashed BIOS on graphics card, then BIOS on mobo, same....this is how it remains, I have renewed all software on my pc, this is why I think it is hardware related, all the same stuff as last install, but it just doesn't perform the same, very jerky graphics.

Someone please help me

Thanx.
Dig.

 

'S ok now, tracked it down to a faulty sound card after reinstalling & "drip feeding" PCI cards & drivers.