BBB power LED & user LED are all not work

Hi
I plug my BBB via USB port with computer.
BBB power LED is not work &user LED are all also not work.

What may it happened?
Thanks

On Sat, 6 Aug 2016 04:34:35 -0700 (PDT), ???
<giwawa8110@gmail.com> declaimed the
following:

Hi
I plug my BBB via USB port with computer.
BBB power LED is not work &user LED are all also not work.
What may it happened?
Thanks

1) bad USB cable
2) bad USB port on computer (is the computer turned on? it is rare for a
USB port to have power without the computer being alive)
3) bad USB jack on BBB
4) fried power controller chip on BBB

Thanks for your reply!
But I check that USB cable is fine and computer is on.Because I just bought this recently.
At first I just connect this board to computer via USB,and it works.
After I connect this board with another board,BBB also connect computer,another connect 24V supply.
BBB not working,all LED not work.
Is there any chance another board broken,so the high voltage go through to the BBB cause it not working properly?

Dennis Lee Bieber於 2016年8月6日星期六 UTC+8下午11時32分27秒寫道:

24v fried the BBB
ITs a 5v only device

On Sat, 6 Aug 2016 09:46:23 -0700, evilwulfie
<evilwulfie@gmail.com> declaimed the
following:

24v fried the BBB
ITs a 5v only device

  And that is only at the point of power-injection (the USB or the
power-supply jack)... The rest of the device is only 3.3V (and only 1.8V on
the A/D converter input). 24V hitting anything likely fried a lot -- even
the barrel jack lacks a regulator that could handle the heat/current drop
from 12V, much less a diesel truck battery.