OK well the crashing at boot hasn't gone away although the fix for it seems to be not to power it off each time but to hit the reset button. This may have been a fluke as it hasn't done it since.

The hard drives are physically fine after doing the advanced checks on them. The only error was a file structure error on the C: drive which I ran a chkdsk /f followed by a defrag.

It has to be a motherboard issue when it fails to even get to the bios screen when powering on. Thankfully its happening a lot less than it was so will just have to live with it for now.