reseating

I reseated my RAM yesterday, but when I turned the PC on, it said it can't post. So I just took the RAM out again, put it back in, and presto, it works normally. I'm just curious - why does this sometimes happen? Seems so simple yet it causes a computer to not POST. Just genuinely curious...

As stated above, the lights on my fans, mobo, and GPU light up, but my monitors stay pitch black. I have tried both monitors with DVI and HDMI with both the GPU and mobo yet nothing works. I have tried reseating ram, CPU, GPU, and replugging the power cables. Something leads me to believe that...

So let me start with saying, I have an RTX card now, but a friend of mine who streams with a AMD Athlon hp pc needs a new system, so i plan on giving her the gpu to sell. The card acted real funny, nothing ive ever seen before. It would prevent boot because the mobo couldnt detect it, but this...

Motherboard: Gigabyte GA H170-D3HP CPU: i5 6500 GPU: Asus ROG STRIX RX 470 4GB; HIS RX 470 IceQ X² OC 4GB RAM: Kingston FURY 16GB (2 x 8GB) DDR4-2400 SSD: Kingston HyperX Fury 240GB 2.5" HDD: Seagate Barracuda 2TB 3.5" PSU: Cougar 700W 80+ Bronze Semi-Modular Wireless Adapter: TP-Link...