Browser connection problem

My mate brought his laptop round with a problem, that IE7 works ok for a short while and the web pages are not available. I loaded firefox and wireless connected to my router but does the same thing.

I have checked connection timeout but that is not active.

Help

Firewall settings?

I have removed the firewall and just using windows firewall

two browsers fail - can you do email or FTP at the time when the browsers aren't working ? Is there a cache server set in Tools/Internet Options/Connection tab/LAN options - if so remove it and uncheck "automatically detect settings".

can the pc ping the router, if so can it ping www.bbc.co.uk- if not can it ping 212.58.224.115

can the browsers access the router setup pages.

The laptop can ping www.bbc.co.uk but cannot view the router, but if I reboot I can then view websites for about 5 mins and then cannot.