@Cal
Agree with catymag, you need to persist and try again [she's using her phone to post at present, hard to give detailed help]. But first you need to READ fully [i.e. UNDERSTAND] the info in the links already given. Some hints: Your unit cannot enter Mass Storage Mode because it's 'bricked', but it CAN enter pre-boot mode [that's the Windows 'ding dong' you hear]. It CAN'T be seen by the PC in that mode like it can be seen in MSM but it is recognised [you can see it's listed in Device Manager]. It can also be recognised by [Only registered and activated users can see links. ] in preboot to check its HWID [correct hwid needed to be sure we're flashing the appropriate cure firmware], OR, because you said you do have a backup just look in Garmin folder for GarminDevice.xml. Open that with a web browser and look for the HWID in there, near start of xml file look for this:
<PartNumber>006-Bxxxx-00</PartNumber> [xxxx is it's HWID]. It'll be either 0972 or 1104 but the former is more common.

We can fix this unit, but you need to get your head around what's happening first. Once you understand it'll be easy-peasy .