The common symptom of this terminal condition, is for the device to be stuck in a loop at the Google flash stage. The device goes no further however long it is left.
So before deciding to install Android Google 5 LOLLIPOP
I recommend you look at the additional functionality Android OS 5 LOLLIPOP is offering over 4.4.4 KITKA, and decide if its worth risking killing your Nexus 7 to have this upgrade?
To give you some idea of how I feel about this, I have downgraded my LOLLIPOP Nexus 7 devices to KITKAT 4.4.4
Also, I am only selling :
fixed1t Android 4.4.4 KITKAT second user replacement motherboards on eBay
for the foreseeable future and I know what I am doing and how to mend these Nexus 7 Android Tablets.
#fixed1tandroidtip