Hi i have this kind of problem, when i connect some load to 5V pin, in my case Lcd display HD44780. Arduino board behaves strange, it keeps disconecting and connecting from my USB port and lcd also isn't working i think there is some voltage drop problem. I used this connection with Lcd display for many months and it works fine but now no. I would appraise any advice.
Please show your schematic.
Note that arduino is not power supply for external modules.
That display will not be the cause of the problem, unless it is damaged. More likely you have a wiring problem, possibly a short circuit. Check for poor or bridged solder connections.
Sounds like a short circuit. A short circuit would cause a large current to flow, triggering the pc to disconnect the usb to protect itself, and, as you suspect, cause a voltage drop.
Please score my advice on a scale of 1 to 10. 
Number 5 
Only 5?
No pleasing some folk.
Appraisal on where you posted you question 0 out of 10
Installation and Troubleshooting is for Problems with the Arduino IDE itself NOT your project. It says so in the description of the section. Therefore I have moved your post here.
You might want to look at this How to get the best from this from this Forum before you proceed any further
Try to power from the barrel ,not usb
I'm cock-a-hoop
That's in base 6, so.
a7
Come over for a BBQ
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