@CJES
Given description of the symptoms, the problem could well be a hardware failure rather than a software or file corruption and hardware would be the most likely conclusion except your device retains the ability to connect in preboot mode. Cure firmware can only help to re-enable Mass Storage Mode (MSM) when a corrupt file, typically a map, poi or voice file, is unable to load on boot causing the device to freeze on the logo screen or endlessly boot-loop, restarting only as far as the logo.

Certain devices such as your 5" nuvi 52 have a tendency to lose the ability to connect to a PC due to weakness of the soldered connections from the USB socket to the PCB, however in that case it's usual that both MSM and preboot connections don't work. Check if the device is being seen in Windows Disk Management, but hasn't been [Only registered and activated users can see links. ]. It won't be given one in preboot of course, but should be given one automatically when in MSM although occasionally it doesn't happen. If you can see the device in Disk Management without a drive letter right click it to add a letter. GarminExpress like Windows File Explorer relies on a drive letter in an MSM connection to see the device. A little info about preboot mode: It's completely normal that a device doesn't stay in preboot indefinitely and disconnects after a short time, only about 10 - 15 seconds for nuvi 52 i think, then show the calibration screen for a while. However it stays locked in preboot if data is sent from Updater.exe then exits and reboots only when the flash has finished.

If you haven't tried a hard reset, then please do so. Be aware that your favorites will be removed and the device returned to most of the original factory settings. To hard reset, hold the screen lower RH corner while powering on then follow the prompts. You can also clear non-vol which is an even more comprehensive reset. To clear non-vol read here: [Only registered and activated users can see links. ].

If that doesn't help then post again and we can go thru more trouble-shooting.