This is the most confusing/interesting problem I have ever come across on a computer. If this is a software related issue it could have something to do with my webroot (antivirus and antispyware) and my bitdefender 2010 (internet security) conflicting with each other somehow. (webroot spyware catches spyware that bitdefender doesn't so I prefer webroot for that advantage). I have been running these two programs for a long time, since Jan 2009, but the problems did not show until late October .
Like some, after trying so many methods I speculated it was a vista update related problem.
Here's my 2 cents: It doesn't really matter how long I browser the internet. Any browser will stop responding. If I browse the internet for just research it takes longer about 6-8hours for the browser to stop responding. If I run youtube and other programs at the same time, eventually the browsers stop responding about 2-3hours. Once the browser stops responding, I can not access heavy website like ign.com, youtube.com, or most links from google.com. BUT I can access light websites, like google.com, imadhatter.com(my professor webpage), eztestonline.com/mycourses.tpx
note: I have not tried uninstalling bitdefender, because the symptoms did not really start from there.
(I can provide screenshots of the issue if you want)