Mac wont boot and fan runs high
Apple's official guide has several good steps. http://support.apple.com/kb/TS1367

I would start with resetting the SMC: the System Management Controller.

http://support.apple.com/kb/HT3964

If that doesn't work, reset the NVRAM (which isn't on the list) followed by attempting to boot to internet recovery.


NVRAM - Command Option P R
Recovery - Command R


Past that, you would need to open the machine and start removing all components that aren't part of the "minimal system" or take it to a technician that does that professionally.