I ran across this problem the other day. I was trying to open my internet browser, it would open and immediatley close. Same thing happened with Firefox.
The error that occured was with the dll file avgxpl.dll. This dll is associated with AVG free anti virus. It was the linkscanner/toolbar they have causing problems with IE and firefox.
If you are having the same problem here is how to fix it.
Make sure to close all browser windows. Open AVG. Click on Overview then double click on the "LinkScanner" Icon. Down where it says "Setting" uncheck all the boxes. Click on sae changes. Close AVG and open up your browser. All should be working you just wont have link scanner abilities.
I am currently running IE 8.0 and AVG 8.5. I will be upgrading to AVG 9.0 to see if this will solve the problem of allowing linkscanner. I will keep people posted.