Why has my Samsung Galaxy S6 gone entirely dark?

[AC Question]

After sending a gmail with 4 photo attachments (13.2 MB) to a friend. Phone has been plugged in to AC for hours. Only indication of power is blue flashing sensor in upper left corner of phone. Checked gmail account from pc - email appears to have been sent successfully.

 

[belodion]

Something may have failed. If after charging, the phone does not power up with a long press of Power, that is likely.
Also, try booting into Recovery.