Hi, my name is ***** ***** welcome to JustAnswer!
Can you tell me what version of Windows your computer is running?
Hi again Roman, you seem to be away from your computer so I'm going to leave some info for you.
It's possible that you have a recovery partition on the system from which you can reinstall Windows. Please see the following link:
You'll want to scroll down to the section that says, "Starting a recovery from the startup logo screen (during system boot)," where it mentions using the F11 key to get into the recovery program.
If that does not work, then you're only option is to get an original Windows installation disc and reinstall the OS from disc.
If you have any other questions on this just let me know.
And before leaving this page, please use the rating box at the top of the page to rate the answer at least 3 Stars/OK Service or better so that I receive credit for assisting you.