Hi there and welcome
Power off the mac
Then start the Mac and hold down the Command and R keys at startup.
Hold these keys until the Apple logo appears. After your computer finishes starting up, you should see a desktop with an OS X menu bar and an OS X Utilities window
choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.
Click the First Aid tab.
Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
Select your Startup Disk (usually named "Macintosh HD").
Click Repair. Disk Utility checks and repairs the disk.
Let this complete and when it has, tell me if you still have the problem please.
When you say didn't do anything, you mean nothing happened? You could not run the repair?
ok, clean up the files in these locations as these are referred to as other
User(s) Downloads folders at ~/DownloadsUser Library caches ~/Library/Caches/User Documents folders ~/Documents/
Let me know how much this frees up please.
have you emptied the trash on the Mac or checked it is emptied?
ok, don't take offense, I never know who I am talking to, from computer professionals to first time users.
download and install Omni Sweeper here
Its going to give much more accurate information on whats taking up space.
Can you see any large files or usage via this app?
the website takes the deposit from you when you first post the question, its a refundable deposit if your not happy, but the deposit is made up front.
I am only an engineer here, you will need to speak to customer service on any payment questions. I know how the site works, but do not handle the payment questions.
You can email them on***@******.*** or call them on 1-***-***-****
let me know if you have any problems