Hi, You can turn system service back on in the BIOS->iDRAC in the lifecycle controller menu. Turn that to enabled.
I have 2 R720 servers clustered with a powervault FC DAS.  I downloaded a bios update, both servers were running 2.2.3 and the update is 2.5.2   The first host updated without a hitch and is running 2.5.2.  The second server fails almost immediately as the BIOS update begins, with error:  Execution Status: System Services is disabled. Any idea what I need to do to resolve this?
R720 BIOS update issue