Flashing question mark, low hard drive space
Though the following should be valid for non-encrypted volumes and unlocked encrypted volumes, it doesn't help much because the main volume here is encrypted and locked. So skip to FileVault2-encrypted volumes

Non-encrypted volumes

Almost no free space on your start volume is a problem. At least 10 % free space are recommended.

It's indeed possible to remove files &amp; folder in Recovery Mode but if you have an external disk/thumb drive (hfs+ or fat32-formatted) you may move them instead:


attach your external device (if you have one).
If FileVault2 is enabled on your main volume start Disk Utility, right click the volume and unlock it
Quit Disk Utility and open /Utilities/Terminal in the menubar
enter cd /Volumes/NameOfYourMainVolume/Users/accountname to change to your user folder (example: cd "/Volumes/Macintosh HD/Users/ausername").
To get the names/mountpoints of your main volume/external disk enter diskutil list or df.
enter ls -la to show all files and folders  

Example:

drwxr-xr-x+ 56 ausername  staff   1904 20 Feb 23:45 .
drwxr-xr-x+  7 root       admin    238 15 Jun  2012 ..
-rw-------   1 ausername  staff      3 21 Nov 16:11 .CFUserTextEncoding
-rw-r--r--@  1 ausername  staff  43012 20 Feb 23:35 .DS_Store
drwxr-xr-x+  3 ausername  staff    102 15 Feb 17:41 .TemporaryItems
drwxr-xr-x   4 ausername  staff    136  2 Nov 23:22 SomeFolder

now move further with cd SomeFolder
enter ls -la to show all files and folders  

Example:

drwxr-xr-x+  7 ausername  staff        238 15 Jun  2012 ..
-rw-------   1 ausername  staff 4736527884 16 Okt 22:33 BigFile.mov
drwxr-xr-x   4 ausername  staff        136  2 Nov 23:22 UnwantedFolder

to move BigFile.mov to your external device enter
mv BigFile.mov /Volumes/ExternalDevice/
or to move UnwantedFolder to your external device enter
mv UnwantedFolder /Volumes/ExternalDevice/.
if you don't have an external drive remove folders and files with rm -dr UnwantedFolder to remove UnwantedFolder and all its content or rm BigFile.mov to remove BigFile.mov (4.7 GB in the example above). rm *.mov removes all .mov files in your working directory.

rm is a powerful command to delete a file or directory without confirmation by default. Because of this behavior, users should really be sure before deleting files or folders. So double check where you are  - enter pwd to print your working directory - and what you want to delete!


FileVault2-encrypted volumes


started to Recovery Mode open Disk Utility



If you had one partition spanning your whole hard drive and encrypted it with FileVault2 it's completely normal that you have only some MB available space left. That's unallocated free space on your hard drive. In the example above 12,7 MB are left.
highlight your FileVault2 volume and unlock it.


enter the FileVault password


if you succeed and the encrypted volume isn't corrupted your FileVault2 volume will be mounted. Check the available free space. In the example below the availbale free space on the volume is 52,8 GB

 

If the unlocking fails - using the correct password - the FileVault2 volume probably is corrupted. The only possible solution then is completely erase/repartition the hard drive and restore a backup.