You might also want to take a look at these:
Windows Support Center – MS Internet ‘Fix It’ – solutions + support from Microsoft
Complete Internet Repair Kit (free) from Rizone3.com - will fix and repair most kinds of internet (including but not limited to IE) problems.
Microsoft has outlined some prerequisites that must be met for a successful install.
Prerequisites for installing Internet Explorer 9
I've also read that once IE9 is installed, the computer must be rebooted twice before opening IE9. I can't remember what site I read that on (might have been CNET or Maximum PC) but the extra minute or two for a second reboot shouldn't be too intrusive on anyone's busy schedule. That's how I installed IE9 on several computers and none of them has any issues. If all else fails Microsoft offers free support (Get Help Now, top right corner in above link.)
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