Thank you Colif. I shall now spend some time running through your suggestions and will report back.Have a look in scheduled tasks and see if anything shows up there that runs 30 minutes after startup.
Try looking in reliability history and see if it shows anything? likely to show Hardware errors about PC shutting down incorrectly, we want to see other ones apart from that. Red X are errors. click on them and in bottom part of window, click view technical details
Try booting into a clean boot and see if it happens - carefully read instructions and make sure NOT to disable any Microsoft services - https://support.microsoft.com/en-au/help/929135/how-to-perform-a-clean-boot-in-windows
if it doesn't happen, slowly add the programs you stopped to start up to figure out which one is causing problem.
At least you had a solution that didn't require losing everything.Colif, I used all your suggestions but could not find the offending program or file. After much time, I decided to go back to a previous clone backup and accept the loss of some data.. But thank you for your interest.