Repair SQL Server Database
Please run below command in your SQL server database to check the level of corruption.If database is showing suspect it wont allow you to run this command


  DBCC CHECKDB (DB_NAME) WITH ALL_ERRORMSGS,NO_INFOMSGS


This command can be used to check corruption in SQL Server database. Also I must say you are running very old version of SQL server if you are not on SP4 your SQL server is in un supported state. If above command returns any consisteny and allocation error there is corruption in SQL server database if not then issue is with backup tool you need to contact vendor in that case.

Best method to recover from corruption is to restore from latest valid backup. You can use RESTORE VERIFYONLY to check consistency of backup before restoring although only successful restore can guarantee that backup is in complete consistent state.

Your other task is to look at SQL Server errrorlog and windows event viewer to find any information related to corruption and take appropriate action. Major cause is inconsistent disk subsystem.

Restoring from valid backup would involve first restoring full backup with no recovery then differential backup(if any) with no recovery and then all log backup witn no recovery but the last log backup with recovery.I you just have full database backup you can restore it with recovery.

How to restore database using SSMS