I changed the service accounts for the following services which are part of my Search Server 2008 Express installation. The Central Administration and Search Administration websites stopped working after that.
Windows Server 2008 64 bit OS
I checked the Event Logs and the following error message was recorded.
"Application Server Administration job failed for service instance"
The above error occurred for the following services.
Windows Sharepoint Services 3
Office Sharepoint Server
I ran the following commands which fixed the above issue and the Central and Search administration pages started working.
1) net stop osearch
2) net start osearch
3) iisreset /noforce