power on problems

I have a pc that I built. It has an AMD 2000+ Athlon, and ECS mainboard. Whenever I turn the power off for more than a few minutes, I have trouble restarting the computer. I turn the power on, all of the fans come on, but it doesn’t do anything else unless I turn it off and on a few times. Sometimes it’s very difficult to get it restarted. What could possibly be wrong? Thanks in advance.