So you are saying that you disconnected a fan and put it back in. then the problem started.
It's properly a connection issue. if it worked before you took the fan out, it's properly something you did wrong.
i had a friends PC that wouldn't start.. it turned out he forgot to put back the 4pin connector to the motherboard.
MOBO: Asus Maximus 6 Hero - GPU: Gigabyte GTX 980ti xtreme - CPU: I7-4770K - PSU: Corsair AX760
RAM: Corsair Vantage 2x4GB - SSD: Samsung 840 Evo 512GB - Case: NZXT H440