Problem while booting Windows 7

Hi my friends.

I have a problem. Yesterday i have installed Windows 7 Ultimate on my laptop. All went right and i used my laptop normal. But when i restarted my laptop, there was a problem with boot, i can't solve it and reinstalled windows again. After installation i used my laptop as previous time, all was ok. While transfering file via skype, my computer freezed and i restared it. After restaring , my computer freezes on boot screen and then restarting.

I dont understand what is the problem? Please, help me to solve it.

Thanks.