Have you reset the router? It's a fairly common problem with wireless systems, that sometimes you need to unplug it from the power source for a minute and then plug it back in to make it pick up again. Some days ours does it frequently, others not so much. At the moment, it's probably been at least a week since I've had to reset, though I can remember occassions where it needed a reset several times in one day.

It's worth a shot, at least, and hopefully it'll help.