MSI Z390 A PRO-BIOS SETTINGS-FF Sake its driving me mad

Hi, i really need need some tech help…Got started to get mining after all the interest for the crack but hit a problem. Not that IT minded but learnt alot, construction is my background… So i geared myself up for a start:
MSI Z390 A Pro motherboard, ime reading and should of gone to ASUS but anyway got one ordered…
Seasonic 1300 PSU…No problem
Intel CORE I5-9600K 3.7 GHZ SKT1151 9MB…Just advised on nett ??
Patriot Signature Premium DDR4 16GB (1x16GB) 3200MHz(PC4-25600) UDIMM W/HEATSHIELD
KingDian 480GB 2.5 inch SSD SATA III Internal Solid State Drive
3 RTX 3090 MSI Supreme X
Anyway, built the rig and followed the setup, GEN2, 4g etc but i cannot get the third GPU online, using 1st PCIEx16 and 2nd PCIE on board. 2 GPUs running fine which is great but for the hell of me i cannot set the board right to get no.3 going,its all nearly ready for the bin as its driving mad.
Any help would be a appreciated…