What PCIe slots do you have them plugged into?
Tried changing all the slots because there are 3 cards, tried using 123, 456, 124, 235 etc.
Looking at your MB manual I would recommend slotting the GPUs into PCIX16, PCIEX4_1, PCIEX4_2 (from top to bottom slots 2, 4, 6) Also make sure the monitor is plugged into slot 2 or PCIEX16.
If it still isn't working may need to change some settings such as changing it all to Gen 2 or Gen 1 in the BIOS.
Thanks, changing slots to 1-3-6 did help for 1 GPU, going to return one GPU as it seems broken or at lease it seems that BIOS is corrupted.