[MENTION=18798]siyasanga88[/MENTION]
The first thing you'll want to do is not use the OC Guru. Go back to stock and OC manually for the best results.
What I like to do is then start to undervolt the CPU. Lower your voltage bit and bit (while running Intel Burn Test and other stress tests) until it is unstable and your desktop crashes. Now we've got your CPU running at stock and voltage is lower so it's running cooler as well.
Now the fun starts - set your bus speed to 100MHz (this makes OCing easier as you'll be increasing the multiplier). Now you can increase your multiplier to 41 (as I believe it should be at 40 - 40 x 100MHz = 4GHz stock clock).
So you've increased your multiplier to 41, giving you a clock speed of 4.1GHz at your lower voltage. Now you can run your Burn Test or other stress test to confirm the voltage is enough to run at that speed. If not, increase your voltage by a small amount (maybe 0.25v) until it is stable again.
All you would need to do is continue increasing the multiplier by 1 and increasing the voltage until it is completely stable.