Wireless connectivity problems

[Tefler]

I have a PC with a wired connection to a router and a laptop which connects to the same router wirelessly. The PC is mostly OK, although the connection fails from time to time and we have to turn the router off to reconnect - why? The main problem's with the laptop. Frequently, but not always, it won't connect to the Internet, giving the message: "Internet Explorer Cannot Display the Webpage". When I run the diagnostic too it cannot find any connectivity. However, the computer claims to have 'excellent' connection to the wireless network and I can ping my DNS server as well as any website I've tried. Repairing the connection has worked, but doesn't always. I don't think it's a firewall problem, as it doesn't always happen, but has even occurred when I've tried turning off the firewall and antivirus. Any light shed on the problem would be gratefully received.
I'm running Windows XP with Kaspersky antivirus and anti-hacker.

[bubbles83]

try accessing your routers et up page and make sure that the router is not set to time out or has any access restriction enabled!

[Tefler]

Thanks, Bubbles. I've tried that, but there's no time limit set up on the router.

I think it must be an IE7 problem, because yesterday I was able to connect to my university website and to Microsoft, but not to Google or anywhere else I wanted to go! Any further thoughts?