Welcome to Mint George1955
An annoying mishap you have
(At least) one of your partitions have got an error and need "fsck"
Reboot with the live DVD and run a file check "fsck" like this in a terminal:
fsck /dev/sda1 where you change sda1 to whatever you have.
And do it for all your partitions
When there is an error in the file system it is mounted read only