[Q] Can't install a rom topic

Okay. So I flashed a rom onto my Galaxy S3 (actually a friend's but whatever) and the camera bugged out entirely, far worse than I expected. Okay, no biggy, so I tried to restore the backup I made. That wont work for some odd reason. I get stuck at the white AT&T screen. So I figured it was safe to assume that I needed a new rom. Factory reset yields the same result. I'm okay with going back to stock rom, I don't really care. I just want it to work again.

I tried flashing a stock rom with odin, which yields this:
<ID:0/004> Added!!
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> I747UCDLK3_I747ATTDLK3_I747UCDLK3_HOME.tar.md5 is valid.
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/004> Odin v.3 engine (ID:4)..
<ID:0/004> File analysis..
<ID:0/004> SetupConnection..
<ID:0/004> Initialzation..
<ID:0/004> Get PIT for mapping..
<ID:0/004> Firmware update start..
<ID:0/004> SingleDownload.
<ID:0/004> aboot.mbn
<ID:0/004> NAND Write Start!!
<ID:0/004> FAIL! (Auth)
<ID:0/004>
<ID:0/004> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)
<ID:0/004> Removed!!
And I cannot figure out how to access the phone in my computer.

I can get into download mode and I have a relatively recent version of TWRP recovery installed. If I can either a) get a flashable rom or b) get into the phone I should be able to fix it.

Any advice appreciated! :)