Windows hangs on boot, i think i'm in trouble

It started today, after i turned the pc on this morning it would go through its normal boot sequence but when it would get to the screen with the Windows logo and message Windows is starting up/logging on it would just freeze at that point, the HDD light does flash but nothing happens. Under normal circumstances i would get a log on screen with log on option for user name administrator (thats me, there is only 1 user account on pc) and request for password, but that screen always stays blank (meaning i cant type anything in) and i would usually get a pop-up message from Windows that says Windows could not log you on, type in password and user name or something like that, and that pop-up has an exclamation point in a yellow triangle. The pop-up only gives the option to click ok which i do and after that i'm taken to a blue Windows screen where where i put in my password next to Administrator since i enable it in User Accounts.But this, i repeat, is the normal logon procedure for me, it could be a problem in itself, i don't know.Anyway, going back to my original problem, that intial logon screen does appear for a split sec before Windows hangs on boot.

Another strange thing i noticed is that the problem only occurs when the pc is turned on after being turned off, not during restart. So i'm able to use my pc cause i hit the reset button after Windows locks up and after i do i log on normally. Same thing happens when i bring the pc out of hibernation by hitting the power button, it starts normally as well.

I'm not sure whats causing this, the only changes i made recently was uninstall the ZA firewall and reinstall AVG antispyware and antivirus.If anyone knows how to fix it please help