In some cases, the label on the device is worn out and it is not possible to extract the model number or serial number by just reading it of the label. If the computer is running Windows 7 or Windows 10, you can use the following commands at the command prompt to extract this information:
wmic bios get serialnumber /format:list
wmic computersystem get model /format:list
To launch commant prompt, click on Windows start button and type command
NOTE: Custom-built computers will not have a serial number associated with them. In this case please use device's universally unique identifier (UUID) in place of the serial number (i.e. in Serial Number and Import Key fields on the asset record form in CMDB). You can extract UUID using this command:
wmic csproduct get UUID
Additional Information
Lenovo - How to find serial numbers?
Dell - Locate your Service Tag or Serial Number
HP PCs, Printers - Finding the Serial Number