Computer shut down automatically and when restarted said
computer shut down due to a Thermal Event

Now when the computer tries to load windows it just switches off

Computer shut down automatically, when rebooted it said shutdown due to thermal event.
Now it will not load windows just switches off

Thats pretty drastic ,apparently you have a bad component such as the Power Supply or MotherBoard , etc. What are your Computer Specs ,Make ,Model . AGE ? Have you added any Hardware recently? If you feel comfortable with opening the Case then you can look for a Few things such as any burnt cards . Make sure the Cooling fans if installed on CPU are working as well as the Power Supply and there are no cables or obstruction in the Blades , Ive seen everything from Hairballs to Ant's nests in em before....

Hi neiljd1,
"Thermal event" shutdowns are usually bad news
It means the temperature protection circuit/program for the CPU ...etc. has shut off the computer (hopefully to avoid further damage).
Hard to tell what caused it.. a failing part ..fan/Power supply/CPU ...etc.
Only thing I can advise is... do some basic troubleshooting & get back to us with more detailed info .
Hope this helps
RGPHNX