Well i've no definative proof, but the only thing that has changed is the graphics card. There are quite a few posts on the AMD forums about this as well, with no fix and no input from AMD. We can't all have duff PSU's and the list of things I haven't done is getting rather short. In the end, I shoudn't have to mess with a card for 12 hours (and counting) to get it to work.
I'll give you my system is old, but I can't find any reason why it should be causing a hard crash when under load that requires a power cycle to fix.The previous card (also AMD) was happy as pie for a long time and when I switch it back it's fine.
I spent quite a bit of cash and waited the best part of 3 months and get 2 seconds of gameplay followed by 12 hours of troubleshooting to get hardly anywhere.
I'm about to flash motherboard bios.