Here is my Solution for you! (Should hopefully work)
Follow this steps:
1st Download this .rar file from
HERE!
2nd Extract the rar in your InfinityMU folder!
What will happen is that the rar will change the current vital files to a 100% Working ones!
So if this doesn't work then we can assume that the actual client isn't the problem!
Please reply with the results!
BTW: I don't think at the moment you should take such a drastic actions as reinstalling the windows!