ASUS m5A97 LE R2.0 Mobo pcie x16 slot won't work, other problems

[storyquest101]

My configuration:
Asus M5A97 LE R2.0 mobo
AMD Radeon XFX R7800 Video Card
2x4 GB 1600 Mhz Crucial Ballistix RAM
2X4 GB hynix Ram
AMD FX 8-Core 3.5 Ghz Processor
Inland ATX ILG-500R2 500W PSU

So the main problem I'm having is that I can't get the pcie x16 on my mobo to work. My video card works fine on the X4 slot, but if I plug it into the x16, there's no display, nothing will show up at all, even though the computer powers up fine.

Also, and even more significatly, I'm having a ton of other problems that I'm not sure are connected with that as well. I significantly upgraded my PC and yet my performance has gone WAY down, and that's with me doubling my RAM and processor capacities.
Mid-level games drag, I have a constant clicking/tapping sound in the audio, games occasionally crash, and just as of yesterday, my computer will just shut down after running for an hour or so.

Other basic things that I think I've ruled out:
I don't think it could be overheating. My tower has 5 fans in it, and nothing feels hot when I turn it off and immediately feel the inside.
I'm not playing high-demand games. The last two games it crashed/shut down with were both over 10 years old, and with my PC at half the power it has now, they ran WAY more smoothly.
My Bios is up to date, I've triple checked that.
It is entirely possible I'm capping my PSU (feedback on that would be appreciated too), but I don't think that would really explain any of the issues outside of sudden shutdowns?

I'm willing to chalk this up to a crappy mobo, but I've already brought one back and replaced it, and I'm having the EXACT same issues, without the slightest difference. Outside of starting completely from scratch with my mobo, I have no idea what else to do. Any suggestions would be welcome.

 

[Lutfij]

1| Never mix and match ram sticks or kits of varying sizes let alone from different makers. Drop either the Hynix or the Crucial ram from your system, whichever was in your system first.
2| That PSU is very dodgy and may very well be the bane of your system.
3| Your motherboard isn't bad, it's the components you've made it run that are the possible suspects.
4| You didn't state the OS that's on your system. You also haven't stated which 7800 series GPU you have as there is a 7850 and a 7870 GPU. You've also generically stated your CPU - what Fx-8000 series CPU are you on?
5| You should use this article to gauge your PSU requirements and this tier list to locate a good unit for your system.