Strange 'jurky' computer behavior... Help pleae!

Hi guys,
My mum has an old computer, it's a Gateway, about five years old and came with an Athlon 1ghz processor. I've since then changed the graphics card to an ATI 9200 and upgraded its 128mb SDRAM. It had started to jerk very often which in a game would cause the graphics and sound to skip and the mouse to move jerky for about 1 1/2 seconds then it would be fine again. This also happens when on the desktop or doing anything else, the mouse just lags for a second or two. I didn't realise until i had a good look at the computer that this happens as much as twice a minute. I added 512 new memory to see if that might help but it still jerks. The computer is running the bare minimum, its used basically to surf the internet and play games, not Quake 4 mind you, she likes those puzzle games you get from zone.com or popcap, not exactly cpu taxing stuff! I've checked for spyware and viruses. It's worked fine up until about 1 or 2 months ago, what could be causing this?

 

What's the power supply rated? If it's that old it might have a 100w PSU, and wasn't designed for a 9200 card, although I think that seems unlikely. I'm guessing she had integrated video before you upgraded it?

Also make sure you updated the motherboard drivers, and I would run ccleaner because that's fixed weird issues with my mouse.

 

Hi Pyrate,
I recently put a 230W PSU in her machine. The motherboard is really, really old and obscure and I can't find a website for it or any drivers, CPU-Z dosn't shed much light either. Ccleaner is a must and I run it daily! I just uninstalled, drivercleaner pro'd and reinstalled the drivers for the graphics card and the problem persists. I'm beginning to think this is a CPU problem as it worked fine as it is for ages, then suddenly problems began. Is there an easy way to test if a CPU is faulty?
Thanks for the advice!