Internet Explorer being shut down due to malicious add-on?

[Sean]

A friend's laptop started acting weird lately. When launching Internet Explorer 8, it would give an error message saying that DEP (Data Execution Prevention) stopped the application from working. I went to the Advanced tab under my system information and made an exception in DEP for Internet Explorer. Afterwards, it just said "Internet Explorer has closed this webpage to protect your computer" and says it may be due to a malfunctioning or malicious add-on. I disabled all the addons and launched it without extensions and stuff, and it still said the same thing. I installed a new antivirus and I found 3 threats and quarantined them all. No malware or anything like that. I even tried resetting Internet Explorer. No help. I uninstalled IE 8 and went back to IE 7. 7 worked mostly fine, and when reinstalling 8, it went back to not working. The laptop is running Windows XP Home SP3. Anyone know what I could do to fix this?