Computer randomly shuts down during Bitlocker prompt?
The cause of the random shutdown is due to some sort of conflict when the disk is formatted as GPT, hence booting through UEFI. Use MBR instead and it should solve the problem.
Exactly what the cause of this conflict is, I have not been able to find out.
Here is what worked for me, I disabled windows' "shutdown at boot feature". In a command prompt window (admin):
bcdedit /set {bootmgr} bootshutdowndisabled 1