Macpro 2012 rebooting randomly, cannot get into AHT

Using both mac and apple keyboards i've tried option+D and D without any luck to start AHT. I simply cannot get into the AHT so that I can see if I have any faulty hardware.

Also in the process of troubleshooting by removing any USB devices that may be cauing any grief (USB audio cards / midi controllers ect) In an attempt to narrow down the issue.

But any help on running a diag on my own would be swell. I've seen others post having issues, in one case the user was given the diag file to replace on there OS. Once done they could then run AHT. I have used this before, but long long ago most likely on an older OS version than my current (high Sierra)

Thank you for you assistance, this MacPro means the world to me. If I can get even a few more years out of it I will be greatful.

Thanks.