Cannot connect to internet

I just bought a nice brand new Studio 1737 laptop running Vista.  I can connect to my wireless network and have excellent signal strength.  However, I cannot connect to the internet.  It worked fine for the first few days, now I pretty much can't get to any webpages.  If I can, they take forever to load.  I have reset (and reinstalled) my router (Belkin N+) and that seemed to work for about a day.  When I hook up with a network cable, everything is fine.  So, it is definitely something in the wireless.  I have also went into DOS and released the IP address, which worked for a few hours.  Does anyone have any other ideas about what the problem is or how to solve it?  I am about to call Dell Support, but was hoping someone else can help first.  Thanks!