Trouble with laptop!!?

K so the story is, i got my laptop brand new and it worked for half a year. a few weeks ago it started acting up and freezing really badly everytime i tried opening google chrome or itunes or some bigger program. Then i turned it off by holding the power button (the bad way), and then the black screen with writing popped up and said, "Windows Error Recovery" and tells me to insert my windows installation disk and restart my computer, along with two other steps. Except, i dont have a windows installation disk. And i dont know what it is. So, i told my school principle about it and he said to re image it. So i got it re imaged like 4 times since my laptop was having problems with connecting to the internet. Its working, but freezing up again and wont let me open things. i've tried opening itunes and it wont pop up. Same with the google chrome. And my laptop is super slow, and it used to be soooo fast! .. but i restarted it the improper way again, and now its saying the error thing again but i can press enter on the start windows normally selection. I keep entering tht mode, but its stuck on the friggen Starting Windows screen. Ive tried getting on several times now, its annoying and no one knows what to do. HELPP!! =[ I payed good money for it.. =[