My computer is failing me

My computer has been randomly crashing lately. I got it built cheaply about a year ago and have replaced RAM, and the motherboard. I have checked the video card and it is fine. I keep dumping money into it and fixing the small problems that it has but it still gives me problems. I do not know why it is crashing right now, I run 4 party tables, PT and PA hud while surfing internet. I have 512 Ram. Could it be my hard drive crashing? To reboot I wait 10 or so minutes and unplug and plug back in and it usually works for a few more days before crashing again. Should I buy a new computer or fix something on this one? I have very very little money, please give me advice on how to remedy this cheaply.