startup failure Pine64

[tllim]

I have PineA64  with Ubuntu image installed on SD card. sometimes it fails to startup and get into OS. the HDMI display recognizes the signal but still shows black screen for a while then back to "NO Signal" message. this happens only on startup.
if I plug out / plug in the power cable again, the system works correctly.
This issue occurs many times.
Any solution for that?
Thx for help,

Please make sure your power supply is not under power.

Thanks for your reply.
Actually, I am sure it is not a power issue. because I tried (5V ,2A ) and (5V,5A) but still sometimes (40%) it doesn't get into system.
check this video please:
https://drive.google.com/open?id=1clDSzg...WLlb3k_YmU
here I am using (5V,5A) power supply!!

Even you uses the 5V 5A power supply, your cable connection seems not able to deliver the 5A current.

Please use multimeter and measure on Pi2 bus "DC in" point to check whether you have 5V supply to your board. If you measure only 4.8V, then please revisit your wiring or use the actual 5V 3A power supply.