I second the heat issue. I had the same kind of thing happen to D-Link wireless router. It was overheating then cooling down. I had it in a tight spot and it wasn't getting the cooling it needed.
Another consideration, (although it sounds like your problem is happening far too regularly for this to be the problem BUT....) Microwaves and wireless phones will knock a wireless router off the air. I had a 2.4GHz phone and everytime my wife used it, I was knocked off the internet. Also for awhile my computer and all equipment was plugged into the same power circuit as my microwave. Again, when the microwave was used, I got knocked off the internet.
Just some food for thought...



