One of the Dell OptiPlex machines were not getting Windows 7 activated by KMS.
I tried running slmgr –ato with no success. Every time following error appeared
Error Code: 0xc004f035. The Software Licensing Service reported that the computer could not be activated with a Volume license product key. Volume licensed systems require upgrading from a qualified operating system. Please contact your system administrator or use a different type of key.
To fix this issue, update BIOS to the latest version available on Dell support site