I have a Kustom KPM4080 PA that I have been having problems with. It's this one pictured below:

A friend lent it to me so I had something to use for practicing with the boys. However it recently stopped working right, and I'm not the in financial situation (see: college) to be throwing down the cash for a new one. I know it's not a high quality unit, but I'm hoping there's something I can do to fix it. It will power on, but no sound will come through any of the channels. If I unplug it and plug it back in, it will power on and work fine for a few minutes but will then suddenly go mute again. I took it apart and poked around to see if anything was loose or something and hit it with some compressed air, and when I put it back together it was doing fine for about 20 minutes...but then it went quiet again and I had to once again unplug it to get it to make a meager few minutes of sound. I am currently only running one microphone into this. Does anyone have any suggestions about what to do to remedy this problem?
god and woody guthrie
you'll find 'em both
in the grand canyon
at sundown