How to access my MacBook's Serial Number
If the main thing you're after is the serial number, you can use Terminal to fetch it.

More specifically:


Launch Terminal
Copy and paste the following command:

ioreg -l | grep IOPlatformSerialNumber
Press return 


NOTE: If the above doesn't work then something strange is going on. However, depending on the model of MacBook, you may be able to remove the battery and check around the battery bay to see if the Serial Number and Ethernet ID are printed there.