If your TWRP's still working and your KF's still charging, you're still in the clear. Try mounting the USB storage through TWRP, upload the ROM to your KF, full wipe, etc.
Oh, sorry I wasn't clear: When I said it wouldn't let me connect via USB, I meant to say that it won't mount in TWRP.
If I click on the icon that looks like a text box in the upper right corner, it says the following:
* Verifying filesystems...
* Verifying partition sizes...
E:Unable to mount '/sdcard' (tw_mount)
E:Unable to mount '/sdcard' (tw_mount)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:Unable to mount /sdcard during GUI startup.
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
E:Unable to mound /sdcard when trying to read settings file.
E:failed to mount /sdcard (Invalid argument.)
E:failed to mount /sdcard (Invalid argument.)
I also can't tick the box that says Mount SDCard. I can tick the other three options, and any time I tap on Mount USB Storage, Windows brings up the You Need To Format The Disk In Drive J: Before You Can Use It prompt.