You possibly have lost the IP from the router
1. if you do an "ipconfig /all at the command prompt that is bring up a DOS window
a. type the command ipconfig /all
b. then type the command ipconfig /release then ipconfig /renew\
you should be connected again that is if you have not lost the connection with the ISP
( Internet Service Provider)
2. check the status of the main router to see this
a. log into the router using 192.168.0.1