Desktop logs on and immediately logs off?

Ok, i've spent hours trying to figure this out on my own. My computer which is a Dell 4700 boots normally, welcome screen appears, click to log on, desktop flashes and logs off. System restore is out of the question fails too restore. Ran in safe mode and i can access desktop with no problem. Ran my Avg in safe mode, Spybot, and System Mechanic 6. No viruses found. But just before this issue started i did run HiJack This, and deleted all reg keys that had no or missing files. Next time i boot i have this problem. In safe  mode i restored all the keys i deleted with HiJack This but still no change.  Can someone plz help!!!!!!!!