My nexus 7 2012 does not start

A

AC Question

It runs KitKat 4.4.4. I switched it off (as it was stuck during browsing) and then it did not open again. I put the charger, I saw the battery icon, switched it on again but it did not boot or open.

I tried any combination with the keys to see the boot loader -- no result. The battery was at about 40%. It seems that there is a hard problem. It did not shut down properly...

Now putting the charger cannot see the battery icon. It is completely dead.
Any suggestion what hardware part could be dead (except the battery)?