First check if the search service account has proper permission on the database. It needs to have 1.Sysadmin 2.Dbcreator 3. Security.
Then check below things
1. Checked to make sure the 'Office Sharepoint Server Search' service
is running on the server on the Central Admin.
2. Make sure that service is running on the search service account.
3. Make sure that service and the indexing service is started under
Control Panel -> Admin Tools -> Services
4. Go to Shared Service Provider properties, select the 'Index
Server' on the list. Add the search service account to the
'Process Accounts with access to this SSP'