horroble hardware lag

I own two computers, both Pentium 4. One is custom built and lets call that one A, and the other is VIAO, lets call that one B. The problem i have with both is that i continuously experience hardware lag where many frames are continuously skipped. On pc A this happens as soon as i start my pc and is not very noticeable, but is very annoying. On pc B it does not always happen, but when it does it is very noticeable, and reminds me of having dial up and minimum requirements for Counter Strike source. If you move the mouse, it takes about 5 seconds to get where i moved it and i don't see the pointer moving, it looks as if though it just teleports. I have run many virus scans on both PCs (AVG and Panda online scans) adaware, spybot S&D, have defragmented, even run registry mechanic. I still can not find the problem. Please help me solve this problem. I can post the details of both pcs only if you tell me how.