Computer doesn't boot normally NEED HELP!!!!

My computer has always done this random thing where it will say that it wasn't shut down properly (but it was) and it goes to the screen before startup when you choose to go into safe mode or last good known configuration ect. It used to be that if you just went in in safe mode and restarted that it would work fine. But that's not the case anymore...if you turn it on it goes through everything fine and it gets to the part where there's the windows logo and then the bar on the bottom scrolling across...but then the monitor goes to power saving mode, and when it comes back on the startup process has reset itself. It works fine in safe mode though. and with networking i can get on the internet fine (hence why i am here :P

I've ran some registry cleaners, clean uninstalls...checked the drivers, whats the problem that it wont boot normally? I would really appreciate if someone knew what was going on, and avoid bringing it into a shop where the guy might not even know whats wrong.

Thanks in advance for any answers that anyone presents.