USB logo on boot (Devo 12s)

Hello! I'm totally new to the world of rc flight stuff and i bought a Devo 12s from someone who was selling his. The guy has put Deviation 5.0.0 on it and it's been working perfectly until 5 minutes ago. I have absolutely no idea what happened, but now whenever i start the transmitter, i get a big white USB logo on the screen even though nothing is connected to it. When i try to connect the transmitter to my computer via a USB cable, the USB logo stays there, and the computer recognizes it as storage device, but it says it is competely full (0 bytes left on 0.98MB) and when i open it, it shows absolutely nothing (even with hidden files shown). I am able to get into DFU mode and when i connect the transmitter to my computer in DFU mode, it also does recognize it. Here is a screenshot of DfuSe:

I have thankfully made a backup of my models and some other stuff yesterday, so i don't really mind restarting fresh if it's the easiest solution.

So what are my options here to get it back working on Deviation?

Thanks in advance for your help!

Re-install Deviation.
Read the installation instructions in the Deviation User Manual which you can find in the sidebar on the left side of this page.
Post here in the forum if you have trouble.

Do i format the USB drive with plain old windows explorer just as if i was formatting a thumb drive or is there a software which i should use to do that? I don't wanna mess up my brand new (used) TX :$