Can anyone help with my web browser issues?

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I am really at my wit's end here. I have tried a number of things, but can't resolve the issue. I have two web browsers on my PC. Firefox and IE 7. Lately BOTH have been horribly slow, taking forever to load pages, giving me errors, and so on. I installed IE 7 to see if that fixed the problem, but I have the same issue on both. This seems to happen mostly with php pages, but I have issues with live journal pages, searches and whatnot as well. I get 404 erros, having to try and load a page 4, 5 times, and all sorts of problems. I've run various tests, pings come back fine, tracenets look good, tried clearing out cach and all that, reset TCP/IP, reset the PC. I've tried FF with and without extentions, in safe mode, new user. I have tried reinstalling FF. NOTHING works. I really have no idea what else to try other then a full reinstall. One thing I wonder is if my NIC is going, and replacing that would work. I belive at the moment I have an onboard NIC, and if an offboard NIC would be better? My current one is about 7 years old, not sure of their lifespan.