This is what I would do:
download hddguru (dont think we are permitted to place links) search in google & use the one that says: -
Download Windows Executable (works without installation):
HDD Low Level Format Tool ver.4.40
put your usb in pc/laptop then open the hddguru program & select your usb from the list & perform a FULL not quick low-level-format (will take 30 to 40 mins for a 16gb pen drive).
Next perform a fat32 format with Windows (FULL not quick, again will take 30 plus mins to complete).
now your usb is in the correct state for the box to read it...
you now need to load an image, to rule out image problems I would use an ATV nightly, search google for ATV nightly & select your box make/model (Zgemma's are listed under AirDigital)
place the zgemma folder on your usb then open the folder, open H3 folder, you will see a file called...noforce....rename this file to...force...save & exit (image will now auto boot when box is powered on).
turn box power supply on at the wall socket (best not to use an extension lead if possible), make sure the rear power button on the zgemma is in the OUT/OFF position...place usb in the rear usb port of the box....
Power the box up by pressing the rear power button to the IN /ON position....watch the front panel of the box....it should show boot....then FLSH....sit back & allow it to flash the box (takes 30 seconds to a minute to flash).
as soon as the box reboots & shows BOOT remove/pull the usb....box will boot up & show the setup screens for 1st setup...continue to set box up using remote & you should have the base functions working, power down the box using the remote (deep standby) then put the rear power button into the OUT/OFF position.
IF all goes well you can then place the usb back in your pc/laptop again & remove/delete the nightly base image then load your backup image of choice on the usb (WBv7 or any other H2S backup build). Place usb in rear port of box & power the box up via the rear button & the box should show boot then FLSH...