That's impossible. Since you didn't tell anything about the what and why ("it does not start" doesn't tell anything about what does happen instead ) I can give just general fixes:
1. System file checker (sfc /scannow from the command prompt)
2. System restore back to when it was OK
3. Back to your latest image backup
4. Reinstall Windows
With more details, also about what went wrong, their might be other suggestions.
Something went wrong with my p.c. Now it does not start in Normal Mode, it only starts in Safe Mode. Can someone give me instructions how to "transfer" from safe mode to normal mode while the computer is working.