Currently Being ModeratedFeb 19, 2013 10:49 AM (in response to drtnz)
Had exactly the same symptoms: Normal start but instead of the desktop building up just a blue screen!
Repair via disk utility was one measure but did not solve the problem. Sould you have a second Mac start the Mac Book as fire wire HD ( press and hold T during start), connect it via firewire to the other Mac. It should appear as an external HD on the desktop! With "command + i" you can check the HD infos and the user rights!
Make sure all say read and write! The box next to "ignore owner..." should be ticked!
To make 200% sure that everything works on the next start up you can create an additional account for user "unknown" with read and write permissions!
After that pull the HD (i.e. your MacBook) into the trash bin, disconnect the fire wire cable and shut down you Mac Book by holding the ON/OFF for about 3 sec.! Now you are ready to restart! Good luck!
PS: If you don't have a second Mac - find a friend with one or try a store selling Apple equipment!