C drive on DELL Laptop 1545

Hello,

Alright , I need big help. my Cdrive is showing that it is full when I check in Properties tab. I try to open it and it says access denied. It won't let me back it up it saying I don't have permission...but its my laptop?? I don't get it..I tried to reinstall Windows 7 from the disk that came with my laptop and it did but it did not take off the Windows7 that was on there so now I have 2 of them, I am wondering if that is most of my C Drive stuff. Can someone help??? I don't care if I lose all the data, I just want my laptop back like it was when I bought it 6 months ago...where it had no problems, I mean I have all my utility,drivers,reinstallation disks...I just don't get it and I really want to smash the thing...but it cost me over 900 to buy it so yeah...i guess I just have to goos fabra it :(
PLEASE SOMEONE...HELP....