My friend helped me build my computer in 2014 (by help I mean did pretty much everything) so I don't know very many technical things about this machine. Today I took out my R9 290 to clean a little dust out of the fans and put it back, but when I played some games I realized I could barely handle low settings when I could easily handle high earlier. I went into BIOS and saw on the motherboard there wasn't anything detected in the space where my GPU was connected. Now I see the graphics card I'm using is Intel HD Graphics 4600 which explains the ****** performance.
What I'm not sure about are the PCI-E connectors for the R9. It seems the only thing that works is connecting a 6 pin and another 6 pin, but there's 8+6 spaces in my GPU. When I try to connect 6+8, my monitors won't work for some reason but I hear the windows start up sound. However if I boot up my computer using 6+6, insert 2 more pins while my computer's running, and restart, the monitor will work. As soon as I plug in those last 2 pins though, my PSU (Corsair CX600W) fan starts blowing really loudly.
So my question is: For connecting my CX600W to my R9 290, am I supposed to use 6+8 or 6+6? And if it's not the PCI-E problems, what else can I try?