Hi, welcome to justanswer.com! My name is Mike.I am going over your question and I will be with you shortly.
OK restart and hold the Shift key until you see the Apple logo. This will activate Safe boot and it will check the drive for errors among other things. It may take longer to boot and you may see a progress bar during part of the process. If it starts up OK… login then restart the normal way from the Apple Menu. Let me know after.