Sounds like a motherboard or other hardware problem, which could be making it freeze. Unplug all drives and all PCI cards so all you have plugged in is the power supply, processor, memory and graphics card. Plug in the monitor and power lead and switch it on (you can leave everything else for now). If it freezes again, see if you can get hold of spare parts to try. If none of the spare parts work, it could be the motherboard. If it gets past the first screen with everything unplugged, plug everything back in one by one until you find the component that's causing it to freeze.
To get your work back, plug the hard drive(s) into another computer and copy it off there. If you've reformatted the hard drive with the work on it, then it will have been deleted and you can try a recovery program to get it back (click here or click here).