As you've flashed QuickCure3 then clearly the device can access preboot regardless of what you're seeing in Device Manager. I'd move to using a cure firmware made with firmware-specific Cure3 before you give in because as i said before QuickCure3 mightn't always work (being as it's not based on the device's specific fw).

If you then still cannot enable Mass Storage Mode likely it has a physical problem and hardware faults cannot be fixed by software means.