UPDATE 
If one of the cheats not work, try on of this links
Wii – http://www.gamesradar.com/wii/guitar-hero-iii-legends-of-rock/cheats-guides-faqs/g-2007041012041714057
Xbox 360 – http://www.gamesradar.com/xbox360/guitar-hero-iii-legends-of-rock/cheats-guides-faqs/g-20070117102232795070
Ps3 – http://www.gamesradar.com/ps3/guitar-hero-iii-legends-of-rock/cheats-guides-faqs/g-200704101203554079
Ps2 – http://www.gamesradar.com/ps2/guitar-hero-iii-legends-of-rock/cheats-guides-faqs/g-20070117102247933076
Pc – http://www.gamesradar.com/pc/guitar-hero-iii-legends-of-rock/cheats-guides-faqs/g-20070911151839209002
I hope this can help
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This video will show you EVERY cheat on Guitar Hero 3!
The music is – In Your Face
by – Children Of Bodom.
Enjoy!! Please rate and comment! Thanks ^^,
This is The list of the cheats for Gh3:
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Large Gems – (Only for Ps2 and Wii)
No Fail – (Does not work in Career mode)
Performence Mode
Hyperspeed
Precision Mode
Unlock All Songs
Air Guitar
Bret Michaels Singer
Easy Expert
Unlock Everything
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Duration : 0:2:31
[youtube OE-v_TlaPpU]