Could you try to boot into Safe mode? Does the laptop allow you to do so?
You could try to restore the system through a repair CD if you have one.
The second thing is to restart your computer, go after pressing the appropriate F key to navigate to the Windows menu. From there you should have access to restore your OS. Open the Command Prompt in safe mode and run the command:
sfc / scannow
Then press Enter and wait for your OS to be repaired. If you cannot access this menu while you reboot, enter the BIOS settings. Then, go to the storage menu in order to verify that your HDD is as at the first boot priority. If it's not, you have to manually set it!
Once you've done this please, let me know what happened. Cheers.