If you are using Desktop, then try to clean your computer ( DUST ).
Take out RAM and re install after proper Cleaning.
Ok well my computer won't turn on, it's an old dell dimension 4500. When I press the power button, it turns yellow, and stays like that, there's no noises or anything. This has happened twice before, it's like, my computer is working fine, but when I turn it off and try to turn it back on, this happens. The previous times it happened, I just left the power button yellow, and eventually the computer just started working within a few hours, but this time it's been almost a week and it's still not working. This is my system info:
Proccessor: Pentium 4 1.8ghz
OS: Windows XP Pro
Graphics: GeForce FX 5700LE