I finally got the bl00dy thing going!
Unbelievably, if you slightly bend the Surface in whilst holding the power key down it will start up. It takes a few goes, but it stayed on long enough on one occasion for me to go to settings and select NEVER SLEEP.
Microsoft, you are a disgrace, you wanted nearly £500 for a replacement, I'll never buy a Microsoft product again, you are no better than a snake oil salesman. Your silence on this issue is shameful.
microsoft bend gate worked for me backing up all my shiz not not trusting this thing again