Applemac107 wrote:
• won't let me sign in— which implies it is started...
Try a SafeBoot How to use safe mode on your Mac - Apple Support will sort many anomalies. Can you log in here?
You can try Internet Recovery Option Command R and run the DiskUtility>First Aid
Boot into Internet Recovery (Option Command R) and from the dropdown menu: Utilities> Disk Utility> run the First Aid on your Macintosh HD (and the "Macintosh HD-Data" volume as well if Catalina/Big Sur/Monterey/Ventura) If errors are found and repaired, run again until no errors reported.
Disk Utility>View>Show All Devices The best sequence is —
Volume level
Container level
Parent drive
ref:
If your Mac doesn't start up all the way - Apple Support
Verify you are plugged into power