4870 Black screen

Recently I have been getting a black screen when stressing the GPU, folding / games ect and CTRL ALT DEL doenst work and I have to reboot, it looks like its turned the monitor off for power saving, this was my thought as I had been messing with the power saving features but I have reset that and the drivers to default and its still happening, also updated the driver with no issue.
Any ideas?

GPU overheating?

I have had the same thing due to heat in the past

Its not geting above 60 degrees and its pretty much instant :/