Hi there and welcome
This is when it is remotely locked by iCloud, it appears someone may have access t your iCloud account.
Can you enter 123456
Is that accepted?
you cannot add anything to it at all?
Power off the mac
Then start the Mac and hold down the Command and R keys at startup.
Hold these keys until the Apple logo appears. After your computer finishes starting up, you should see a desktop with an OS X menu bar and an OS X Utilities window
choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.
Click the First Aid tab.
Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
Select your Startup Disk (usually named "Macintosh HD").
Click Repair. Disk Utility checks and repairs the disk.
Let this complete and when it has, tell me if you still have the problem please.
On which step did you get to?
yes but did you hold the keys down when booting as I requested?
start the Mac and hold down the Command and R keys at startup.
ok, please attempt the following
Hold Apple+S when booting to enter single user mode
Enter int eh below press enter on each line#sh /etc/rc#passwd yourusername#reboot
1) Insert the OSX install disc that came with the MacBook.2)Re-start the MacBook and when you hear the chime sound hold down the ‘C’ key.3)Choose the proper language and hit continue4)Now you will be at the installer. Choose Utilities and then Reset Password.
Let me know the results please
ok, power it off then on and hold option + command + R at the chime
what then happens?
is it a wireless or cabled keyboard your using?
ok, do ypou have the Mac installation disk with you now?