8 Krypton

Dell Precision 7510 TB16 Boot Issues

So I got the TB16 to use with my Windows 10 Precision 7510. I've had issues with the USB devices dropping out randomly but I seem to have got that under control (for now). I'm having another issue of sorts. Updated the BIOS then went into the BIOS changed restart/shutdown to "thorough" and checked "thunderbolt adapter boot support" and "thunderbolt adapter pre boot modules" as I wanted to boot from a USB DVD drive that was connected to the TB16. But when I tried to boot the laptop got stuck on the Dell logo and wouldn't go into POST. I tried diagnostic boot and got the same result. Couldn't get far enough to press F2 or F12. When I disconnected the TB16 and powered on the laptop it booted up fine. I could then connect the TB16 and it would work fine. But if I tried to restart with the TB16 connected I had the same issue. I eventually unchecked "thunderbolt adapter boot support" and "thunderbolt adapter pre boot modules" just so I could restart without having to disconnect the TB16 (I don't know which of the two options is causing the booting issue though). I can get by without booting from the TB16 but I got it partly for that reason so would to get it working if I can. Any ideas?