my Arduino does not turn on. I am running and Arduino uno r3. it turns on sometimes, but not others. PLS HELP!
Let me see....
Hm, no clues.
You need to give us more information. How do you "turn on" Arduino? Using USB or a power supply? Do the onboard LEDs turn on or not at all? And when you connect it to your USB port, does the device come up or not?
PS: Also that "sometimes" is too much vague.
when I unplug it from my computer, it turns off. I don't know why. its dumb.
like anytime I use the round plug it doesn't work..
What? If you unplug the USB where do you think Arduino could get energy from?
The "round plug" with what? Are you using a power supply? And what kind of it (e.g. the DC output voltage, the max current, and barrel polarity)?
the barrel plug when I use the wall plug.
I always have the two pluges in together.
sorry if bad english I am using Google translate.
There's no reason for doing that, anyway, if you have both plugged in, unplug the USB and then Arduino turns off, something is wrong with the power supply and/or its cable and/or its plug. So, what are the specifications of your power supply? Are you sure it's correct? Can you try another power supply?
And do you have any other device connected to Arduino, or this happens even with a bare "naked" Arduino?
I still wonder if there is a reason when sometimes it seems to work and when not...
i have a nothing connected to it.
You should describe "it"... which could be many things.
Did you use your Arduino in any other projects before now?
yeah. I made a water sensor with the rain sensor.
The barrel jack is connected to a voltage regulator. Your wall adaptor should be at least 7V.
it supllies 9v
Ok, so, what about switching to another power supply to see if it's the culprit?
And/or plugging another Arduino, if you have more than one, and see if it works, under the same conditions?
And I'm still waiting for a better description for "it turns on sometimes, but not others"...
okay I used the plug from my Alexa and it works now without any turning off thank you guys so much!
Thank goodness for Christmas / New Year, the season to launch new ICT / STEM careers.
Good for you, but bad for Alexa 
(besides, it shows the culprit was the power adapter or its cable you were using...)
Buy a new standard power adapter (tipically 5V 1A output, with barrel plug) and give the poor Alexa her power back!
hahaha will do 
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