Windows vista wont startup. PLz!! help im freakin out

I recently shut down my computer, then when i i logged on it took like awhile to enter, then their was this green screen and no computer icon or starmenu just a opened folder. the computer folder to be more specific, so i tried to open a program file and then the comman prompt open up and then closes making it impossible to open any program, so i cant run my anti virus because of this nor the internet. i also tried in save mode but it also doesnt start there. im unable to do anything cause of this, the only thing i can do is turn the computer off and restart it.