Download a copy of Netstumbler. This will then show if you can see your wireless router.
I had an issue where the router worked with the wired PC but not to the laptop over the wireless. Took the laptop for a walk, and Netstumbler confirmed that there were other wireless networks available, is the laptop card was enabled and working.
It also confirmed that the router was not. After a period of OFF the router was then seen to light up but there were gaps in the signal/noise display. Because it was gapping the laptop could not get a lock.
The ultimate solution was a new router. This gave much better results until one day it too went tango uniform but a regular period of OFF and it worked ever since. I now control all my computer mains adapters using a remote control socket and knock the lot off when I stop for the day. This also lets the lot cool down and the router and printer to reset.