I need help, not sure if its the right place to ask but im gonna take a chance.
This weekend ive been building a 6700XT rig out of a Open Air Frame Miningcave open air frame The motherboard is a b250 BTC P12 (or 250b in the bios)
The rig came pre-installed from miningcave with Hiveos, and with no card in it, it work flawleslly I can go on hiveos, I can do the update & upgrade (what I did)
but as soon as im trying to start the rig with the cards (6700xt) in it HiveOS just wont boot and ive got a blank screen, but the rig and run and look like its physically running normally, ive been on this since Friday afternoon and I cant seem to find any solution
Here what I tried that didn’t work 
:
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Run it with one card
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Upgrade & update Hiveos to last version
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Try different GPU Risers
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Completly Reset motherboard unpluging GPU and taking battery out
Here what work and bring me to HiveOS 
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Starting the rig with one or many Nvidia card
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Starting the rig with no card
Only thing im thinking that could actually help is so update the BIOS but on that card ive got no clue how and where.
Since the rig come from miningcave ive sent them a message on FB to see if they have a solution, it must be possible because they sell 6700xt rig with those parts
Anyone has an idea, im really getting desperate and I need some sleep