Can you boot into Safe mode?
I have an idea and it is to restore the system through an installation CD/USB if you have one. You can make a bootable device on another PC that has similar operating system as your PC – I mean 64 or 32 bits.
Please, 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. There, navigate to the storage menu to verify that your hard drive is as a first boot priority. If not, set it!
Once you have done this please, come over here to tell me what happened.