I had the same problem updating from 5.6 to 6.0.
Suddenly the server went down and I could not connect, not remotely
and not even local. The computer didn't go off.
What helped for me was to disable the power savings in the bios of the server.
For some reasion the server in 6.0 didn't wake up on LAN activity or in 5.6 the server
never went into power-saving state.
Maybe this helps for you to.