I have no idea what sudo is. Sadly this is what I expected with Linux. It's like someone using Windows for the first time and expecting them to use Command Line with no guide. I'll have a go at what has been suggested and report back. Thanks for the comments.
Can you check the inittab file to see what runlevel you are booting into? At the prompt again, type: cat /etc/inittab to see the output. Near the top of the file, there should be a line similar to:
Where the number 5 is above, you should see a 4 or 5, not sure about Mint. If it 3, change it. Need to use sudo to edit this file: sudo gedit /etc/inittab.