Computer Problems

Hey everyone if there's no post for a couple days I want you guys to know why. My iMac G5 is having power issues. It keeps shutting down when it feels like it. I was going to take it in but I took it apart and cleaned it and got all the dust out of it and it started working again. But now if its on sleep to long it shuts down. So pretty soon I'm going to be taking it in to get looked at.