just try 1. put your windows CD and see any response???
2. try to press F8 at the time of booting???
3.any thing installed any error messages earlier?? already checked your RAM,MB,FAN and all correct?? do on more thing if their is any dust around their clean all including all ports...if all these methods failed...may be chance for a hardware booting failure may be HD...because MB working fine with all L8 indication @ bottom???try and tell me lets clear it ok i will also search for your answer if its not resolved....