Yes back when you converted from UEFI to MBR you lost the ability to use secure boot and UEFI. Converting to MBR works there is no way to convert a OS SSD to UEFI with out a clean install
The solution is to clean install windows 8.1 or 10 PRO in UEFI mode See the sticky thread on the procedure
https://rog.asus.com/forum/showthread.php?76993-Guide-How-to-install-windows-8-8-1-10-The-proper-way.... And bit locker is only available on the pro versions of window.
I don't know who would know what version of UEFI your notebook supports it came UEFI. This is the first time I have every had the version of UEFI come up Perhaps some other users of Bit locker may have more information I would troll the MS forums on bit locker ? I don't think many gamers use it.
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro