First, did you make a Restore Point when you made these changes?
Secondly, FTM2011 Will work with MSIE9, but there is a Script Error that many have seen, after MSIE9 was introduced in March 2011. So, going back to MSIE8 isn't a bad thing.
What is missing here, is a little more details about what you are seeing when you re-installed FTM2011.
Did you do an Install or did you do a Repair?
Did you see any errors when you did this?
Are you seeing any error messages now?