You can try some of these in Safe Mode - repeatedly tap F8 as you boot.
If you do not have a Windows 7 disk you can borrow a friends as they are not copy
protected. Your System maker will also sell the physical DVD cheap since you already
own Windows. Also you can make a repair disk on another computer.
Try Startup Repair - (If at ANY point you gain some but not full access to Windows come
back and try Startup Repair again.)