I bet it's your flash addon/plugin installation. Check which versions you have installed in your Control Panel -> Add/Remove Programs (Programs and Features for Win7). It's possible you may have multiple versions installed, but you can uninstall all of them, then install the latest by going to http://get.adobe.com/flashplayer/
I have the same problem on my workstation at work, the Flash ads constantly f*** all my browsing windows when I get a bad ad on NASIOC.
You can confirm this by pressing "CTRL + ALT + DELETE" and clicking "Task Manager", then under the "Processes" tab, check for processes running with "flash" in their name and see if they're using a lot of memory. (alot meaning, possibly using 100,000+ K)