When you deleted the messages etc., did you just hit "Delete" or did you bypass Trash? If not, and they're in the Trash, you haven't actually gained any space.
The problem is that without a lot of space, the graphical user interface doesn't run right, or at all. It's recommended (but not clearly enough!) not to let your disks (ie partitions) get fuller than about 95%.
The way to deal with this is from the recovery console because that avoids loading the GUI. Boot your system, but choose "recovery mode" instead of the usual one. If you have an ethernet cable, plug that in, and when it gives the six or so booting options, choose "root console with network access". (If no ethernet, don't worry about it. It'll just give you an error message but boot normally.)
The prompt will look like this: #
You will be in root's home, not your own. To delete your own Trash from the command line type
DO NOT MAKE ANY TYPOS. Especially do not put any spaces in the path. For instance, "rm -rf /home /your-login-name/etc would delete all the home directories on your machine. The "rm -rf" command, running as root, will allow you to delete your entire hard disk, or any part of it, without a single "are you sure?" question.
rm -rf /home/your-login-name/.local/share/Trash
Another huge space hog is nautilus' thumbnails. They can safely be deleted too, and will be rebuilt as you need them.
When you're done deleting things, typeto restart the boot process.
rm -rf /home/your-login-name/.thumbnails/
If a full Trash was the problem, this should at least give you enough space to boot normally again and to go on with the deleting process in an easier environment.