In reply to Tom Hutton:
These symptoms are normally indicative of incompatibility between the MTU (maximum transmisible packet size) detected by the network card/driver in your PC and the actual packet size allowed on the connection from the router to the outside world. Especially if your broadband connection uses PPPoE, the additional overhead will reduce the packet size from the default 1500 bytes -
if this is the cause, the question is why it has suddenly changed?
Unless you like to play around at the command prompt level to confirm the problem, your best bet is talk to your ISP and find out if they have changed anything.