1. Power off, pull the AC line and gently reseat all cards, memory sticks and cables. DON'T TOUCH the CPU! It's the model that you could crack the CPU core if you put too much pressure on it.
(try again.)

2. The makeup of the machine would be interesting to know. Guessing by symptom and age would have me look at the motherboard capacitors to see if they are failing. Here's the article and pictures. http://www.pcstats.com/articleview.cfm?articleID=195

3. Next is the power supply. It's not as good as it was new. I'd beg/borrow about a 400 Watt Athlon rated PSU and retest.