Timeshift snapshots occupied a 2TB harddrive. I wasnt able to delete them so i downloaded gparted and formatted the harddrive, i also made a new partitiontable with ext4, but i didnt mount it. While the next booting i wasnt able to access the gui, only the command line for service needs. I researched a little bit and tried with the mount command to mount it again or to unmount it finally from fstab with unmount and --force. doesnt help, i cant boot into my system anymore. I have two ssd with 240gb and 2 2tb hdd i have a dualboot system, on one of the ssd's there is a windows10 on the other the elementary os. I can access windows10 without problems.