I just bought one used from ebay, with the seller stating that he had run benchmarks on it before sending it to me to test if it was working. Fastforward to yesterday, I get it in the mail. First thing I put it in my rig and right when booting into windows, the screen artifacts horribly and then it just goes black. Upon rebooting, the OS isn't detecting the graphics card and is using the integrated graphics from the processor. I've already tried reflashing the BIOS, which only lead to the same previous thing occurring once more. Anyone have any ideas on how to fix this?
Also, for some reason it is detected by HWiNFO64 but doesn't display much information about it and only detects 1024 mbs of gRam?

I'm pretty sure that it would support; Intel Core i7-4790k, 24gb of ram, 750W EVGA NEX PSU, Z97 gaming 5 motherboard from gigabyte
 

Sounds like you got sold a defective card. Time to start a ebay case to get your money back, rma the card if any warranty is remaining, or if you want to try to fix it you could try baking the card in the oven.
 
Note: Make sure you bake the card with the die facing up instead of down.