When that happens, hit Ctrl + Shift + Esc, go to the Processes tab, select "Show processes from all users" checkbox on the bottom, and click the CPU header column to arrange in descending order of what processes are taking up the most CPU percentage. This should tell you what's going bonkers at that point when iexplorer is freezing up. It could be a number of things, but you should check that first to make sure it's actually IE causing the issue or whether it's something else (an add-on or third party program integrated into ie).