This is close. Don't know if this helps. 

I was getting the some error when I upgraded to *Mathematica* 9 from  *Mathematica* 8 on Windows 7 64-bit. It crashed right when it was **initializing preferences** ( as displayed on the spikey icon). (But the kernel was working fine, if I manually launched it from the start menu. I could run some calculations on it as well).
I deleted the preferences folder [http://reference.wolfram.com/mathematica/tutorial/ConfigurationFiles.html][1]). Then I reinstalled  *Mathematica* 9. After that  *Mathematica* 9 works fine.

( Sidenote 1 : I checked my comp for viruses. Incidentally my comp was infected with some virus (as reported by Malwarebytes anti-malware). I removed them. I am not sure if this was the cause for this problem.

Sidenote 2 : I still have my  *Mathematica* 8 installed and working and this was working even when   *Mathematica* 9 was not working )


  [1]: http://reference.wolfram.com/mathematica/tutorial/ConfigurationFiles.html