ubuntu mate cannot boot when usb drive plugged, anyone can help?
How do you power the board? PSU specification?
2A PSU power on directly or through reboot command both will fail
is this a Harddisk and if so, can you put an external PowerSupply on the Harddisk and does it work then ?
If it is just an USB-Stick, what is on that stick or is it clean fresh formated with EXT3 or EXT4 ?
a Harddisk with a NTFS part and a ext4 part
can you put an external PowerSupply on the Harddisk?
if not, do you have an USB-Hub that has external powersupply ?
And try now to boot.