Kindly go through the listed options:
The SQL Server Instance That Will not Start
Service account password incorrect or account locked or disabled.
Corrupt or missing master database files.
Corrupt or missing model database files.
Unable to create tempDB.
Unable to open the error log
If files are missing or corrupted for system databases (master and/or model) SQL Server service would not start. ERROR LOG (mentioned earlier)would contain the exact database name and file name which has the problem