It could be anything from a bad add-in to a virus. You will have to give more details.
A good start is to diagnose whether add-ins are part of your problem, Internet Explorer 7 comes with a No Add-ons mode. You access it by going to Start, All Programs, Accessories, and System Tools. Select "Internet Explorer (No Add-Ons)" and see if the problems you've been encountering are still present, without all of the add-ins running. If indeed the problem is resolved without add-ins involved, then it's time to figure out which one is causing problems. Start IE7 the normal way, and then from the Tools menu, select Internet Options and then the Programs tab, and then click the Manage Add-ons button. Select an add-on from the list, and then click Disable. Lather, rinse, repeat as necessary!!!!
[navy]When I married "Miss Right" I didn't realise her first name was 'always'. LOL[/navy]