Windows starts after restart, but not after shutdown

I have a very strange problem, my Windows doesn't start after I shut down and I have to go to Startup Repair which does nothing, but from that screen I can click Restart and it starts without a problem.
After it starts if I restart it works, but if I try to shut it down and then start, it does not work.
I have some critical events in Event Viewer that state: "The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly." Task category: (63), but when I shut down it doesn't apear to be any problems.

Any help would be much apreciated.

When you say Startup repair does nothing, do you mean you tried it but it didn't help?

Try running SFC /SCANNOW Command - System File Checker

I used Startup Repair and it says it can't automatically fix startup problems.

Try Startup Repair again from a Repair Disk and also your Installation DVD/USB.

Did you run sfc /scannow yet?

I tried that already and it still says that it can't be fixed automatically. But Windows starts even though Startup Repair says that, if I click restart. If I shut down then push the power button it goes to black screen and after manual reset I can launch Startup Repair and click restart to access Windows.

I haven't run sfc /scannow, I'll try it later today.

Have you checked your CMOS battery? It sometimes causes problems if the time resets itself. How about the time? Do you have to reset it every time you boot your comouter?

When Auto Startup Repair says it can't solve the problem, click on Details and look for the issue.

Also, you can shutdown the machine, then start it up, and go back to Events Manager and look for the latest error.

The first thing I would do though, it a capacitive drain-down. Shut the machine down, remove all powered peripherals, the ac power, and the battery if it's a laptop, then hold the power button down for 20 secs. Let up for 10 secs, then press again for 5 secs.