Since Avant Browser runs off of the Internet Explorer engine, there might be a problem with that.
If you can, uninstall Internet Explorer 7 (through Add/Remove programs). Then use the System Restore and restore your computer back to a time before your friend installed Internet Explorer 7. System Restore can be accessed by going here: Start >> All Programs >> Accessories >> System Tools >> System Restore.
Happiness is not about being perfect.
It is about seeing beyond the imperfections.