Well, i recently installed Ubuntu 14.04 in a HDD of 640 GB capacity. After the installation, I decided that i should partition my HDD so to have on the one partition the os and some other files (320 gb) and save to the other partition my video-edit works (320 gb). And I did so using the Ubuntu 14.04 live cd and gparted. I formatted the new disk part "with" ext4. But then something wird happened: While i am using ubuntu without any problem, i cannot edit the second partition, which means that i can't save or create something there! Ubuntu says that I am not the owner!! Why?? I need to solve this immediately!
EDIT: Both of these two solutions below worked for me! However, faster way proved to be the one I have chosen!