Perpetual Reboot / Kernel Panic
If it most often hangs during fsck then I would lean pretty hard towards it being a drive failure. Also, resetting the PMU could be worth a shot. Does the battery hold a charge?

If so, shut down, unplug from charger, wait 5 minutes, seriously wait 5 minutes, then boot from the battery. shut down after boot, reconnect your power adapter. Boot. Notice I wrote shut down specifically and not re-boot. Give that a try.

As far as the fans going full blast- this is normal for safe mode boot.