1.) Try running sfc /scannow from Start > Run to see if any files are corrupted. (leave a space between sfc and / )

If that doesn't fix it try the following.

2.)How many sticks of RAM are you using?

If you're using more than one,remove a stick and power up.If you still get a crash,replace the stick and remove the next one.Continue removing/replacing sticks until you no longer get the crash.