The finder is the magnifying glass at the top right.
Or, its the icon on your dock at the furthest left. its easier to use the magnifying glass though..
And then type in disk utility, and launch the disk utility app.
On the left side of the disk utility window, click your mac hd, then at the upper right hand side click first aid, and run first aid.
Once it says first aid complete.. Shut down your mac
Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R.
Turn on your Mac.
Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
Hold these keys until the computer restarts and you hear the startup sound for a second time.
Release the keys.
If the mac tries to start, shut it down again. Then, press and h old the left shift key while you start the mac..
That should put the mac in safe mode.. Can you sign into your normal account now?
Senior Technician and Network Switching Systems Operator / Maintainer.