Hard locks almost always indicate a hardware problem.
1. If you are overclocking set ALL clocks back to stock (Memory, CPU, & GPU)
2. Reseat ALL connectors. Don't just push on them, actually remove then reinstall.
3. Double and triple check that the processor heatsink is properly installed and square to the CPU. Clean and replace the thermal compound when you do this (only a VERY thin layer of compound).
4. Make sure that you have the 6 or 8 pin power plugs connected to the video card.
5. Disconnect all external devices except mouse, & keyboard.
That fixed it, thanks very much!!