I know this is probably in the "duh" category, but do you have your router in a place where any cooling vents are blocked? Is the power supply or the router in an area where it may get hot?
If it operates intermittently, you might have a power supply problem. it it's an external power supply, a trip ro Radio Shcak with the old power supply and fifteen bucks may solve the problem.
If you have a voltmeter, you might check the power supply and see if the volts are low. Test it, then bump the power supply sharply and see if the volts are the same. If the reading changes, or if you get readings that are low or that change constantly, you may have a problem.