Vista - wireless internet connection

I have a desk top I bought from Dell less than two years ago. I installed a wireless connection to the desk top about four months ago. It works fine when I first turn on the computer, but if the computer has been turned on for more then a few hours, it will not connect to the internet. It will connect to my wireless connection. what I mean is that I can connect to the network I set up with the wireless router, but it will not connect to the internet. I thought it was the router, but my laptop works fine all day and the other older desk top I have down stairs works fine all day also. Any ideas on what could be wrong? I do have the work around of shutting down the computer for an hour or so, or just shutting it down multiple times. Any help would be great.

thanks,

I don't have a solution but have you checked all your Power options to make sure there is nothing turning the connection of after a certain time ?