Why does my internet keep disconnecting?

I’ve had this problem before, usually it just reconnects after a while—> if i turn off my computer, or right click on my Wireless Network connection thing and click “repair”. But this happens so often now. About every 5–10 minutes (or more)it disconnects, it gets really annoying. What is the problem? I’ve even brot this computer to PC Place.. some computer store, and they charged us like 70 bucks. They only cleaned it and said it was dirty, but i doubt that this is the computer’s problem, I think it is the network connection. In the past, I’ve phoned them a bunch of times for this exact problem, they turned the thing up till the signal strength was high… but even at that point, it still disconnected on me occasionally, but now it’s happening a bit TOO much! =\ Does anyone know wut’s wrong with it? and What should i do?