MacBook Pro freezing and restart not helping

My MacBook Pro was working just fine until recently. It started with some slow loading on Safari. Then Safari started freezing. I would force quit and it would be fine. I restarted, checked updates (there aren’t any). It got worse the last two days. Now when I startup it gets to my home screen but not matter what I select I get the rainbow wheel and it doesn’t respond. I try to force quit and that takes forever and eventually Safari or whatever I was trying to do will open. Then the rainbow wheel comes back again. I tried restarting and pressing command R to check the disk utility and run first aid on my hard drive but it shows it is not mounted. (I don’t know what that means). Help!