I am having the same problem with the port being greyed out. I have an arduino mega 2560
I am running a dual boot 64 bit laptop with Ubuntu 15.04 and Windows 8.1. (Port is greyed out in both)
I have tried all of the suggestions I can find on the internet and I have so far had no luck.
in windows I have tried device manager and if i plug in or unplug the arduino there is no difference in the usb file, so I guess it is not being detected.
In Ubuntu
I have tried different usb cables
I have tried running as root using sudo
I have tried adding myself to the dialout group
I have tried searching for ls -l /dev/ttyACM0 to give myself permissions for serial out but I get the error No such file or folder
I have also tried ls -l /dev/ttyUSB* with the same results as above
I have tried dsmeg and the arduino is not found
I have tried lsusb and still arduino is not there
I have tried arduino 1.0.5 from the ubuntu software center
I have tried arduino 1.6.5 as a direct download, un tar'd the file and set it all up in the correct folders.
But still nothing
every other aspect of the IDE seems to work except for being able to upload to the board.
The board works ok as I can use it on a desktop PC that has windows 7 and Ubuntu 14.04
I would prefer if I could get it working on the Ubuntu partition as I use that on the most and is much faster than Windows
any other ideas on what I can try would be appreciated
Thanks
Update
Turns out the board was at fault! after buying a new mega all worked fine