In the Services Management Tool, select Restart for ArcGIS Server Object Manager service.
You can use this for resetting the Esri ArcGIS Server Standard system completely.
Note: Restarting of the ArcGIS Server Object Manager (SOM) service may work quite fast. Anyway, it will take some time till all Server Object Container processes (SOC) managed by SOM are up and running.

ArcGIS Server Object Manager - Restart