Hello noobie needs help with stone age pc

Hello, im a moderate experienced computer user who has done just about everything he knows(hehe not so much) to retrieve his stoneage old computer. Let me be a litle more specific i have owned a piece of junk Compaq presario for the last 4-5 years. Since it was my first ever pc i was in love with it for a year or so then i came to learn the truth about my pcs dark side. Behold! Its CPU was an amd athlon tbird aka devils stove(  i made that up). Anyways not long after i ve learned about the overheating issues and this and that. As i was expecting i started to have these problems within a couple of years. Over heating issue got so bad(at the time i had no clue on to deal with it)after about two years i burned the mobo and the cpu. However i wasnt gonna just dippose my 1000$ investment instead i had someone replace my motherboard and cpu with similar ones(Uwave&athlon tbird 1.2). Now after 2 years its acting up again and not just acting up but fucking up big time. However lately its been getting really confusing. Whenever the computer overheats(or whatever the problem is) when i mess with the HDD ide cables, such as removing or switching them between primary and secondary it boots up again. And if that doesnt work i remove the CPU clean it up with some rubbing alcohol and then put it back in it sometimes boots up. Or listen to this, once all i had to do was remove the one of the two rams i had and it booted up. After its boot i put the ram back in to see if that was the problem but it booted up fine after like 3 hours of surfing the web and some gaming(cs) it crashed again. I have no idea what the hell is wrong with it. So to solution to this i have bought an other compaq (call me a dumbass i deserve it) but that turned out to be a junk too so i returned it. I have been wanting to build my own pc or get an apple but since im on a tight budget i think im gonna stick with building a pc. However i wanted to keep my old one alive so i could create a network and play some lite games(cs mostly).