Mountain Lion upgrade problem after CPU upgrade

Hi guys. I have 2011 imac 27inch i5. I have a problem with upgrading to Mountain lion just after putting i7 2600k cpu upgraded last night. It was fine when I upgraded CPU and restarted the system. I had bit of web browsing and video editing stuff. Once mountain lion was downloaded I clicked it and it restarted but never come back. just keep restarting and restarting. is that because some of the original parts were upgraded and Apple knows it is been modified in some ways? Im not so sure what is going on. I tried Recovery USB booting and was successful to see the Utility page where I can reinstall fresh copy of OSX LION. but it also fails. please help me out guys. anyone has the same problem?