Thanks to everyone who tried to help. I'll never know what went wrong. Because it is a new computer i just done a factory reset. It has worked. I hope it never happens to anyone who has files to lose. Once again thanks to all that tried to help.

Glad you've got it fixed. I have now done a google for this and come up with a few items like this one.

Seems the disparity could be due to a driver issue. So, if a driver had recently been updated it could have caused the problem. When redoing the the updates after your factory reset you may hit the issue again - if so I would check if the video drivers are one of the updates and if so go and get the latest drivers from nvidia/amd/intel (depending on which it has).

could be a.net update.

If .net gets an update then windows has to compile its files, for some reason .net isnt distributed pre compiled.

It does 2 lots of compiling, the first high priority ones are done immediatly and the 2nd set is done later when the machine is idle. On a high spec machine with say 4 cores it will still take at least a few minutes, on a single core laptop it can take hours.

You are not the only "user". The computer is a "user" as well and processes are happening all the time.