I believe an earlier post picked up on your problem. It sounds as if your wireless card is not waking up after hibernation.
When you do a restart on the computer, does the wireless connect? If, after hibernation, you can unplug the wireless card and plug it back in, and it connects, it indicates the card isn't waking up.
Likely not a router problem, but a problem in setup of the wireless card. Have you looked for updated drivers or setup software for the card?
If it worked before, you might try removing the card and then deleting the drivers. Shut down the computer, reinsert the card and boot up. The drivers will reinstall.
