Update firmware DEVO 7E

I'm attempting to upgrade firmware for Devo 7E.
My tx goes into the 'Prog. Update mode ok' by pressing the 'EXT' while turning it on and I have the upgrade tool and it works fine, recognizing my DEVO 7E. And I have figured out how to upgrade the necessary dfu file.

However,I can't go to the next step to format the tx via my PC and to cut and paste the necessary updated filesystem into it.
A uTube clip shows that turning on the tx while holding down the 'ENT' button will allow the PC to recognize that a removable device (my tx) is available and accessible to format and add files. However, that doesn't happen on my Tx. and there's no recognition by my PC.

Has anybody got the answer to this prob?

You have successfully updated the firmware? USB is not available with stock firmware so if upgrade was not successful you can't go on.
Please switch the tx on without any button pressed. You should not see too much on the screen - if so, the upgrade was correct. If the stock firmware starts, do the upgrade again - do not select UPLOAD in dfuse screen (this will destroy the firmware file on your pc so you have to download it again) but select UPGRADE.
If you have upgraded to deviation USB filesystem should be available. It is reported that other USB devices can prevent the pc from recognizing the tx, but as far as I remember only with dfuse, not with file system.

If the error is still there please report exactly waht you have done (and which versions you used).