Currently Being ModeratedApr 11, 2013 9:05 AM (in response to Raucousdog)
There is no such thing as 2009 G5. The last Power Mac G5 was introduced in 2005, doesn't have an Intel chip, that's what the G5 indicates, an thus can not run Mountain Lion. You probably have a Mac Pro (Early 2009).
In any case, did you try doing a SMC re-set: http://support.apple.com/kb/HT3964?viewlocale=en_US&locale=en_US