Nexus 7 in Fastboot (recovery) not activating USB connection
Have you tried putting the proper drivers in the right locations on your filesystem? This has been an issue with my Nexus 7 as well, and was solved by acquiring the proper drivers.

Also, it seems from your fastboot screen information your Nexus is fairly custom at this point (product name usually reads grouper, the device codename, yours seems to call itself FLO?). This may affect what drivers are required, but I am not an expert in driver compatibility. Perhaps, due to the ambiguity of what can be flashed to the fully unlocked Nexus line, you may actually have pushed Nexus 4 firmware to your device, and due to the fact that they differ only in size, it may appear to you to still be running the software for the 7.

It appears your device has, in the fastboot information, a slot for reading to the user what carrier the device is currently subscribed to. This should, to the best of my knowledge, only appear on the Nexus 4, or the GSM capable 3G enabled version of the Grouper (Nexus 7). It can be very easy to push the files for your phone to your tablet accidentally, and might be worth consideration.

If you have a WiFi only device, this is likely the issue. A quick way to discern if you have the Nexus 4 software on your Nexus 7 is to run an application that has a user interface which is programmed to change from the phone to the tablet (a list of such apps should be easily found with a Google query. I believe Gmail is one, but that may be blurry for us with the Nexus 7 because it is considered a "Phablet", a hybrid style device).

I recommend trying to erase all Android drivers on the host computer, and reinstalling the specific drivers for the Nexus 7 only, then after hopefully solving the issue, redownload the other necessary drivers for other devices, only after this issue has been resolved.

If that is not helpful, I would consider a full overhaul of your system through pushing a Google supplied system image through adb, and using recovery partition to erase everything and reinstall stock flavor of this device. It may also be possible fully through adb, since you say it is detected when using that utility. Hope this helps you somehow :]

To sum it up, you either have interfering drivers, or have given your device its cousin software from your phone, a very small difference in terms of observable functionality assumably, but large for accessing the fastboot function.