Browser hangs

I have an Inspiron 1720 with Vista Home Premium SP2 and am having trouble with browser 'hangups'. The problem occurs regardless of the browser (Firefox, Opera, and IE), and can happen anytime from after 30 minutes use up to several hours. The browser just doesn't respond anymore and the process can't be killed with the task manager. I've run virus and malware scans and the notebook isn't infested. Any suggestions?

mpr327