I installed Win7 Pro on my wife's PC last week. Every once in awhile IE seems to lose it's ability to connect to the internet. I can still connect to other PC's and the file server shares. I can ping other machines on the network and I can ping sites on the internet but IE will not connect to the site. Once I reboot it works fine for a few hours and then it starts all over again.

Any ideas?

P.S. I installed Firefox and have the same problem.

You should use winsockfix program. I had the same problem when working for one company, and it solved it. Download link here:
http://usfiles.brothersoft.com/utilities/network/WinsockFix.exe