I tried to update my Mac with the latest software. I didn't back it up and now it is frozen on the white screen with the apple and it just spins. I tried rebooting and it didn't help. I hope I didn't lose all the data on the Mac. Help
Bootup holding CMD+r, or the Option/alt key to boot from the Restore partition & use Disk Utility from there to Repair the Disk, then Repair Permissions.