Ubuntu is freshly installed. I have had the same problem several times and re-installed Ubuntu in order to fix it. I have a Dell Inspiron 13, on dual boot with windows 10. Ubuntu is on an external HDD.
I install dropbox through the software center and reboot.
Then, when if I have both skype and dropbox running, Skype logs me out at a random time. If I try to log in it says that I am already logged in in this computer, but even if I quit Skype and relaunch I have the same problem. When I reboot, the system does not boot and gives me a command prompt. I run
fsck on the
/boot partition, it fixes the problems, and if I try to launch dropbox the system prompts me to re-install the daemon.
Then again, if I launch both Skype and dropbox I have the same problem.
For the moment I uninstalled dropbox and the system seems to work fine, after several reboots. Any idea what might be wrong with dropbox?