Did you go into the router configurations and see if it somehow got set to only allow certain computers to connect? If it did, you'd have to enter each computer's MAC address. If it isn't set up like this, it should be, unless you want any random person with a wireless card to use your connection.

Also, you could check to see if there are any firmware updates.

Oh, and as for Linksys, they don't have a terrific track record either, especially since Cisco bought them. A lot of people seem to get disconnected pretty often on both wired and wireless Linksys routers. I think that Linksys, Netgear, and other home router manufacturers need to seriously improve their quality assurance departments.