Alright, thanks a million. I couldn't find a ftf specifically for the SGP512, but according to this comment a specific SGP511 ftf will work as well.
I'm guessing Flashtool is pretty self-explanatory (it looks pretty straightforward), but if not, I'll be back .
Thanks again!
---------- Post added at 09:19 PM ---------- Previous post was at 08:56 PM ----------
Well, I must have done something wrong.
So, I got Flashtool to recognise the device exactly as you said. However, Flashtool didn't have an option for showing/opening ftf files, so I disconnected the device. I then Googled the exact procedure (and felt like an idiot), found it, and wanted to reconnect the device.
No luck. All I get now is a blue light when I press volume-up and connect it via USB. Flashtool recognises nothing. I also turned it back on into the bootloop, pressed the red button, and tried again - no luck. Any ideas?
If the device has a blue light, then that mean it's in fastboot mode. Try reconnecting it by holding the volume down button. This should have a different color and put it into flashmode. In flashtool select the big lightning icon, then select flashmode. Then click the '...' in the top right and point flashtool to wherever the downloaded ftf file is. Then select flash.