Error when going to OWA

This may be a certificate issue.
Check event viewer and also run get-exchangecertificate| fl.
Check the validity of all certificates and renew if needed.
If its a 3rd paty CA you should consult them, if not renew it and restart the MS Exchange transport service.

Also check the same by accessing owa from other machines too..

Cert is valid. restarted the service and still have the issue

have you run iisreset /noforce.  

which servvice did you try to restart?

did you try to restart the information store or the system attendant?  If those are giving you issues, check DNS, and/or remove IPv6 from the machine (disable it through the registry)  If IPv6 is not used in your network, and it's enabled on the exchange server, it could cause issues with Exchange seeing AD, thereby causing issues with those 2 services.

Please check if default web site is working using https://localhost  &  let me know

In powershell run

Test-servicehealth

Look for any services not running and restart them with start-service <service name> my test rig won't automatically start several services and the behaviour is like yours.

Sorry this is assuming exchange 2007 or later

Outsourced IT fixed it