Is this an early 2008 MacBook Pro?
I observed two of these machines work perfectly for several months (different users and workflows) with no issues and with normal shutdown. The next press of the power button is greeted by about 3 - 5 seconds of DVD click, hard disk seek, and then nothing. Different batteries, chargers, and memory chips were used with no machine revival.
As these two machines were fully depreciated employer hardware, they were scrapped, rather than provided to Apple for hardware diagnostic and likely expensive repair.