[Nexus 7 Q&A, Help & Troubleshooting] spl140:
As per the title when booting my Nexus 7 the google logo appears, then the animated circles appear, where it then stays stuck indefinitely. Not rooted and OS version is ~5.1. I can get the exact number if needed I think....

Others have encountered this issue but not in the utterly baffling way that I am:

I cannot get fastboot mode to work so that I can try flashing to fix it without wiping my data as per this post: https://forums.androidcentral.com/goto/post?id=3262838

I can enter fastboot/bootloader mode on powering up or restarting the tablet, but none of the PCs I have tried plugging it into recognise it having done so: I get the error

"Device descriptor request failed" on a windows 10 machine and on windows 7 and vista machines, it just says it's an unknown device and immediately errors when I plug it in saying it failed to install the device properly (on all 3 machines). I have tried plugging it into multiple different USB ports on multiple different machines with multiple different cables, still get the same behaviour.

In the device manager device properties, I can see that it cannot resolve the device ID, it just says "USB\DEVICE_DESCRIPTOR_FAILURE" and I can see the device path is "USB\VID_0000&PID_0002". Having looked at another thread on this site, that would imply it's a hardware issue, and maybe it is but it doesn't feel like it (this is where it gets weird):

If I switch on the device without going into fastboot and let it get stuck on the circles, then plug it in to my Vista laptop the machine correctly recognises it and adb, at least partially, works. I.e. The following commands work:

adb devices -l shows device ID etc and doesn't show it as offline

adb -s [Device ID] shell getprop shows what appears to be all the available properties with seemingly sensible values (not failing to resolve most of the properties)

adb -s [Device ID] shell pwd shows me at device root directory which I think is about right

As well as PWD "ls" and recursive ls commands work, so it lists all the available files that don't have special permissions set on them, not just system files but also my personal data in the emulated directory.

I can copy files across using the adb shell pull command as well, so it seems I'll be able to rescue at least some of my data, although I'd like to get hold of my chrome bookmarks, which I'm not sure where they live or how they're stored so if anyone does know much appreciated if they can enlighten me.

I can also shutdown the device with adb -s [Device ID] shell reboot -p

What doesn't work is adb -s [Device ID] shell list packages

It says the command isn't found - (Android Debug Bridge version is 1.0.32, maybe a bit old but would a newer version actually add any functionality that can help me rescue the tablet?)

I haven't tried all the adb commands exhaustively but clearly at least some work ....

Any ideas how I can fix the overall issue given the above?

Could it be possible I can fix fastboot to work on my PC given adb is somewhat working at least (i.e. fix the bootloader partition/files)?

Or perhaps get a log file to pinpoint the exact issue causing the getting stuck on flying circles and fix it by tinkering with some startup/config file somewhere? Or maybe the device can be flashed via ADB instead of fastboot somehow and I can switch the OS image to a working one without wiping my data.

Perhaps Skipsoft might be worth a go even though fastboot doesn't work and it looks like it needs that to do it's magic? There's also the 15 second adb installer script which some folk have had success with but that also feels like it needs fastboot.

Looking at other threads it seems a factory reset is far from guaranteed to fix this issue so I would like to not do that if can be helped, even though I am at least partially able to back up my data.

Any help would be appreciated.