Kindle Fire not recognised by computer (already tried factory reset)?

Kindle Fire 1st Gen

MOBI files (could also convert to AZW3)

No "official" Kindle USB, just some generic cellphone USB that happens to fit the Kindle

I downloaded a series of books I love that are in MOBI format and added them to Calibre. I've got a sort of OCD issue with having the files show up in the DOCs folder instead of the books, so I did everything I've read about that should allow the Kindle Fire to read those files as books.

I've tried sending them to my @free.kindle.com email, but they still show up as DOCs, regardless, so I decided to just use a USB. Now, I don't have the original or "official" USB that apparently came with the Kindle, but I've heard that any USB that works on generic cellphones will also work with the Kindle, so I found one and am currently using it. When plugged in, the Kindle DOES say "You can now transfer files from your computer to Kindle", and it stays like that unless I press "Disconnect", but the Kindle isn't showing up on my computer ANYWHERE. I've tried resetting the Kindle and the computer, as well as resetting the Kindle to factory settings, but nothing. It seems to show up on my boyfriend's computer just fine, but he HATES downloading anything on his computer or really plugging things into it... so I can't use his.

Is it the USB, maybe? I used a generic USB at his house and it showed up just fine... maybe it's my computer?

My mum has two Kindle Fires, one she uses, and one she doesn't... so maybe I should just trade my current one in for her unused one? Do you think that could work? I really REALLY want those books on my Kindle as BOOKS, not Documents. It's annoying as, and I just want to read them in a clean format.

Thanks so much!

P.S - and PLEASE don't tell me to reset my Kindle, my computer, or do anything else that involves "resetting" anything. I've done all of it several times. I'm beginning to think my bloody Kindle just despises my computer.