Mac Not Fully Loading...

I think I overloaded my Mac. A while ago, I started getting a notification telling me that my hard drive was full and to free up some space by deleting files. I kept clicking okay thinking I'd just delete some files later, but I finally downloaded a song and when I tried to restart my computer it wouldn't fully load.

I get a blue screen and the same notification telling me to delete files. The menu bar at the top doesn't show up initially, but when I press the play button, I get a notification saying that iTunes cannot be opened, and when i click play and drag the cursor up to the top, the menu bar appears. I can use the menu to get to recent items>safari.

Certain applications work, like safari and pages, but I can't open itunes or get my mac to recognize any external devices. I can't open finder, either, so I don't know how I can delete any files.

I even tried using the installer to restore my computer, but I didn't have any space left to install it.

Can anyone help?

Thank you so much!! My mac is back to running like normal!

and I think I'll definitely start listening to the notifications….