If the problem was caused by overwriting bootloader, you will still need to flash something in place of it. You can try flashing the first file here:
Updated versions linked a few posts below
This is the same bootloader that is used on newer devices, so it supports updating with MIDI SysEx instead of DFU. Normally it gets written from firmware, but it's ok to just flash image directly. If you can boot from it, you won't need to use DFU at all. If it works and firmware is OK, you should get everything working. If firmware is not flashed correctly, it should return to bootloader mode (OWL-BOOT midi device name), then I'll upload sysex image to flash firmware without DFU.
Note: you must use 0x8000000 address for bootloader, not 0x8008000 that is used for firmware.