When viewing the console output of your instance, if the following content is returned then you need to check the integrity of your data on the root file system.
Checking filesystems Checking all file systems. [/sbin/fsck.ext3 (1) -- /] fsck.ext3 -a /dev/vda3 / contains a file system with errors, check forced. /: Inode 226708 has illegal block(s). /: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY. (i.e., without -a or -p options)
To do so:
Stop the instance and unmount the volume.
Mount the volume on another instance.
Run an fsck on the volume.
Remount the volume on the original instance, then launch it.
For more information, see Viewing the Console Output of an Instance.