21" iMac mid 2011

OSX Lion

issue:

- happen after I install osx update, mac stuck on the white screen after the apple logo + loading

troubleshooting:

- unable to enter safe mode, stuck on white screen
- able to enter recovery mode
- check the write permission and disk, all seems fine
- reset PRAM
- hardware test, OK

I have no other idea accept for reinstall the Lion can u have a look on this? kindly PM me. thanks.