I don't know what systems you are using, i.e. xp, vista etc. Are you wireless? If so check your connections, I run xp , go to start click and then click connectors, this will show if you are getting a signal from your router.
You may need to reconnect, their should be a box in wireless connections where you can click repair.
Another thing is if you have a back up browser such as Internet Explorer try that, I use I.E. but have had trouble in the past, so I keep fire fox as aback up so I can get on line and fix I.E. hope this helps