Connect to the Administration interface of your router and then perform a factory reset. If I am right, the problem should disappear. However, if you're connection through wireless, go to Wireless > Wireless Advanced and make sure that the channel is 11 and the transmit power is 100 %. Do not modify anything else or you'll have problems with the connection. In most of the cases, a simple factory reset fixes common errors such as network interruption, browsing speed, etc.
