Hi, without knowing the model number it's a bit hard to be precise.
There are a couple of things you can try.
1) Power it off for a minute then let it reboot, might simply be a bit confused this should sort it out.
2) If the router is the type with removable ariels for the wireless ensure these are attached to finger tightness, if not tighten them :) If they are slacken them off and retighten.
3) Make sure the aerials are actually stood upright, laying them flat really reduces the range they can transmit over.
Apart from that it's correct try a different frequency band.
If you've recently physically moved the router, move it back! it's in a poor place for reception.