Server Lifecycle But Still Providing Unidentified Services

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http://serverfault.com – I have this older HP ProLiant server that needs to be lifecycled, but there are still some services that are apparently running on it. There are only a few workstations that are being serviced by this particular server, but it not a DC, DNS or DHCP and whenever I shut this thing down, I get calls stating the workstations are bogged down to the point where users cannot even utilize the system whatsoever. So, I turn the server back on and the workstations are back to normal. It is the strangest damn thing I have ever seen. How would I go about troubleshooting this issue? Thanks (HowTos)