As long as no settings were changed, ie. Workgroup names, IP addressing , I might:
1) Shut down everything and reboot in this order: Modem>>Router>>PCs. See if that gets you back.
2) Firmware update of the router.
3) Spyware/online viral scans.
Need help on getting a LAN working between two XPSP2 computers working again. Worked ok, but quit. The computers are routed through a Lynksys BEFSR41 router. A DSL modem is also connected to the router. One computer is a notebook, the other is a desktop.
All lights on the router, modem, and the computers are lit correctly. I can get access to the internet from either computer. The desktop recognizes on it's own screen only what is marked as shared, and doesn't see the laptop. The laptop only recognizes the router and cannot see the desktop. The laptop only displays the router and not the files it shares.
I can ping each computer from the other successfully by ip address, but not by name.
I have tried a new router, with no change.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic