If you did all the normal procedures (PRAM, disconnect the HDD to see if boot w/ just CD, logic board reset, etc.) you just may have a hateful drive or a bad burn.
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MacBook 2GHz Intel Core 2 Duo w/ 2GB DDR2 RAM & 120GB SATA 5400RPM HDD
Canon Rebel XTI
Google Cr-48 Beta Laptop