My suggestion would be to check connections on
a. Motherboard - the 24 pin ATX cable
b. Motherboard - the extra 2x4 CPU cable
c. Gpu 3x8 or 1x12 power cable
d. PCI slot - card is well fitted?
e. PCI riser cables if used - most of them are El cheapo quality and won't work - Corsair gen 4 with...