You haven't overclocked it properly at all.
Start slowly, check for stability as you go, etc.
Read the stickies.
Don't just crank it up a gig and then say "Something went wrong".
Don't know if this will save you reading the stickies, but here's quick and dirty instructions.
Take memory out of the equation - For AMD put it at 333, slacken the timings. For Intel I haven't a clue - I think just slacken the timings because you can use the multiplier on Intel?
Put it up by a couple of hundred mhz, and then run Orthos for half an hour.
Put it up by a hundred, run Orthos for half an hour.
Then go up 50 mhz at a time until you hit a problem.
Bring it down by 10 mhz until you don't hit any problems.
When you find something that works for 30 minutes, run it for 2 hours to check it's stable.
Up the volts by 0.25.
Starting from where you had it overclocked to, up it by 10 mhz and run Orthos until you hit problems.
Once you have the highest your CPU will do, then try and get the same speed but with your memory running faster. Keep the slack timings while you do this.
Once you have the highest memory and CPU you can get, tighten the timings as much as they will go.
Once you have that done, then do your graphics card.
Yes, it takes a while.