I ran into an issue once where a new install of Ubuntu wanted to partition my drive to no more than 200GB.  From the command terminal run sudo df -h to show your diskspace allocations.

Another issue you may have is that bitcoind is already running in the background.  If so you won't be able to run bitcoin-qt, nor will you be able to start bitcoind from the terminal.  Did you set up a systemd file so bitcoind will start on machine startup?