update, replaced the M2. with SSD, no change, also CSM on or of does not change anything. also UEFI vs. Legacy seem to be not a factor. With 3 cards it won't post at all, just a black screen
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You need to determine if it's a display issue or boot issue, Any difference in beep tones if your MB has a speaker? Does it respond to a ping?
I assume you've tried different cards in different slots to rule that out. Do your Teslas have display output? Check those if you have no ouput from iGPU.
Don't forget about VM. Try a different OS.