Hi Roy,
first can you check your cables and connections are sound?
Do you notice if a particular app keeps running?
Try booting into safe mode by pressing F8 when booting up and see if the machine will shut down
Please open start menu, look in all programs for command prompt, right click on it, choose properties and then run as admin. Type:
sfc /scannow
Press enter and await results.
Run a malware scan (free):
Anti-Malware for your home and for your business