The Macbook Pro from 2008 literally had a thermal issue. It made some units not boot at all. And it required a logic board replace, not just a software fix.
"If the fans run at high RPMs, but the computer does not boot, there is probably an issue with the thermal sensors.
Late 2008/Early 2009 models feature a thermal sensor on the heat sink. First, ensure that the thermal sensor on the heat sink is plugged into the logic board. If it is, try replacing the heat sink. If this does not fix the problem, the logic board most likely needs to be replaced."
The Macbook Pro from 2008 literally had a thermal issue. It made some units not boot at all. And it required a logic board replace, not just a software fix.
https://www.ifixit.com/Wiki/MacBook_Pro_15%22_Unibody_Troubl...
"If the fans run at high RPMs, but the computer does not boot, there is probably an issue with the thermal sensors.
Late 2008/Early 2009 models feature a thermal sensor on the heat sink. First, ensure that the thermal sensor on the heat sink is plugged into the logic board. If it is, try replacing the heat sink. If this does not fix the problem, the logic board most likely needs to be replaced."