Strange Boot Problem - BBB doesn't start, Power LED not (!) ON

One question to the experts:
I had a running BBB-Board (Rev.C) with a Linux-System running Debian from the eMMC, …
I was connected via Ethernet and configuring the system via ssh-Terminal-Connection.
The last thing I tried has been some ethernet-configuration and the restart of the inet-services with
" sudo /etc/init.d/networking restart ".
Some minutes later I was’nt unable to restart my ssh-connection (BBB still working), so I tried restarting the system with the reset-button (seems to doesn’t work well, so I did a hard reset by pressing the power-button for a few seconds).

The result is now:
The BBB does not start, if I disconnect the 5V-Supply and reconnect (short and long pause tested) I see a short flashing of D1 (Power LED), nothing more. Always if I press the Power-Button, I get the same result but nothing more, too.
I already tried to boot from a sd-card with suitable image without success, too. In difference to others (in this or other newsgroups) the Power LED is not “always on” but “nearly always off”. :frowning:

After a look into the electronic schematics it looks like a problem of the IC U2 (TPS65217C) for me.This IC should deliver all the supply-voltages and LED D1 is directly connected to VLDO2 of this Chip.
So what could be the Problem, how to solve it? I found a reset-Pin of this IC U2 which is not connected - does it make sens / is it possible to reset this IC?

Thanks for your help in advance.