You have an 'N' series. The non 'N' series Optiplex 990s and 790s are already SLIC 2.1 compliant. To unlock the 'N' series, NORMALLY, using svctag and ASSET from a DOS-bootable USB stick would unlock it via ASSET PASS:12/31. However, this doesn't work with the newer Dells with UEFIs. You need SmMfgCfg32.exe or SmMfgCfg64.exe to do so, and so far, these utilities haven't come up on the net yet...