SQL Server “Suspect” database?

First thing is to make sure you DO NOT detach that database. Restoring from the last known good backup is fine. Otherwise, you will need to use the EMERGENCY repair mode (I am assuming you are running SQL 2005 or higher). Here are a couple of posts from Paul Randal on the subject. Read them both before you start taking any action.

Here are the steps to Fix the SQL Server Database Suspect Mode Error

• Step 1: Bring Database Online in EMERGENCY MODE.
  
• Step 2: Perform Consistency Check Using DBCC Command DBCC CHECKDB.
  
• Step 3: Bring the Database in SINGLE_USER Mode to ROLLBACK TRANSACTION.
  
• Step 4: Take a Full Backup of the User Database which was marked Suspect Before.