Help required to get me back to 4.00GHz

Hi All,
When I bought my rig Jan 2010 the CPU ran at 4.00GHz but it has gone back to 3.33GHz. I haven't a clue why.
I have since added an SSD, GPU and memory etc but never over clocked anything before in my life.
Can someone help me to get back to my 4.00GHz?
Many thanks.
Rig Spec:-
Intel Core i7 975 Extreme 3.33GHz Bloomfield.
Mobo - Asus P6T de luxe v2 Rev 1.xx
RAM - 6 x 2 GB OCZ3G2000LV6GK
GPU - Asus 560Ti 1GB
SSD - Crucial C300 256 GB
CPU cooler-Scythe Mini Ninja
Case - NZXT Hush Black Gamer
PSU - Coolermaster 620W Real Power Modular
O/S - Windows 7 Pro 64 bit SP 1 on a SSD 256GB Real C300 Crucial
For backup etc I have a 1.5TB SATA 2 Samsung
I have a 24 x Dual Layer Optiarc DVR/RW Optical drive and a LG Blu Ray RW and DVD-RW L/Scribe optical drive

That should be a pretty easy overclock with that chip. First, go into BIOS and look for a presaved overclock configuration for 4.0GHz. If you bought it already overclocked, they may have been nice enough to save the configuration for you in the BIOS. If not, no big deal. For a mild OC like that, nothing more than a slight Vcore bump should get you stable once you bump up your BCLK.

Hi Deltafan909,
Many thanks for your reply to my query.
I have searched the BIOS cannot find any saved profile. Under Tools tab there is a place for "OC Profile configuration" but "nothing installed".
So I am hoping that you will kindly explain in greater detail what you are suggesting I do to get back to 4.00GHz.
The bus speed of my rig is 133.6 MHz. The multiplier is 25. The core speed is 3340.9 MHz. Core voltage is 1.208v.
I am a silver surfer as they say and only started with computers recently!
Could you do a step by step guide applicable to my situation? I would be most grateful.
Many thanks.

Here is a great way to start. http://www.overclockers.com/3-step-guide-overclock-core-i3-i5-i7/

After going through this, feel free to ask questions.

That guide is really long, I suggest to get to 4 you try a 200x20, no change in vcore, and do a few stability tests. If that works, you saved yourself a lot of time.

What speed is your RAM? 1333, 1600..? Keep your mulitplier at 25, and increase your blck to 160. Increase your vcore to 1.25-1.30. Whatever your think, I'm not sure how the 975 vcore range is. I would probably bring it right up to 1.3, stress test with prime for about and hour or two. If stable, decrease vcore a notch, stress test, repeat. Keep a keen eye on temps.