Are you dual-booting with Windows? NO
Which edition of ZorinOS are you running e.g. Pro, Core, Lite etc? Zorin OS 16.1
Can you edit your profile to indicate that there, as it will save that second question being asked again in future.
When you installed ZorinOS did you turn off (UEFI) Secure Boot and Windows Fast Startup. See this thread Before you install i didn't that
even when I am trying to start any application after restart my machine it's took around 3 to 4 minutes