I don't know exactly what went wrong, but I just opened up my case to switch out my power supply (EVGA 1000G) and put in a new GPU (Sapphire Radeon r9 290), got everything all situated, turned on the system, and it's working great... the only anomaly is that it's not recognizing the old Western Digital HDD I use for storage of pictures, music, and games.
The system recognizes my SDD that has Windows installed just fine, as well as my CD-ROM drive that's also hooked up via SATA cable. I even tried plugging the HDD into a different SATA slot, thinking I may have accidentally damaged one, with no luck.
What could the problem be? I know it's not too little power (what with a 1000W PSU), and I don't see why the GPU installation would interfere with a hard drive... is the thing just fried, or something? It's not the biggest deal if it is, as I have a 500GB SSD on the way any day now. Though I would like to salvage this HDD because there are a few pictures on it that have sentimental value.
More about :sata hdd recognized windows installing gpu
Does it spin? Does the bios see it? Check the settings in the bios, make sure it is set (if it has that setting) to ahci, not legacy. Also check the voltage of your 12 volt rail. Some hard drives get finnicky and wont run unless its real close to 12 volts.