On a SQL Server, you can hunt down your event logs (may be security logs) and search for SQL Server service account and find some information related to it as when and who locked it. It does have a MAJOR IMPACT if SQL Servers that run under this locked account have rebooted. Server (OS) will start but SQL WILL NOT START.

So check your event logs and check with your AD Team as well as Gail suggested. Also, her suggestion regarding diabling interactive login of service account is very valid. It is very important.

Thanks,

Vikas