Webuser Forums: unable to get some website

I have been using a router/modem combined (LINKSYS wag325n) for sometime will no problems on any websites at all. But i went to get onto today it would show my home page YAHOO .co.uk but when i wanted to get on other site it was no good at all. I use firefox as my browser and this problem was on firefox and internet explorer. I reinstalled the router and all the setting but the problem is still there. When i plugged in my old modem ( one i got from my isp) everything was ok all websites works ok no problems. But on the wireless side of the router everything works ok as my son has a wireless link to the router. I have switched of my ant virus and the build in firewall in the router and it was till the same. the window firewall is off anyway. can anyone help me with this problem. shane