Network Problem

Here in my office we have 13 computers on a network, 10 of which are brand new. One of the old computers has trouble opening some pages, specifically yahoo. Other computers open up the page instantly whilst on that computer it won’t even load at times. I pinged the router, there 0ms lag. Google opens up like a dream. Maybe I need to change the network card? I tried changing IE settings, and installed Firefox, neither of which helped. The computer was formatted only 2 months ago when I set up the network, and I don’t allow anyone to install software on the computers, so it should be working fine. Anyone able to offer a solution?