There isn't a magic bullet. You need to sit down and tune the queries. If you have no idea where to start, consider hiring someone who does.

Then I hope you don't need your backup, maintenance plan and job history...

Stop SQL Agent

Set the DB into single user mode

Run CheckDB with the repair_allow_data_loss option. You will lose data...

Got a backup of MSDB from before the corruption occurred?

Sure, there's several ways. The group by's the simplest.

Max over partition, row number over partition with a where...

No.

In future please post new questions...

Why?

Then ask your DBA to give you permissions to take backups.

Don't understand about the restore. Backup files don't have mdfs and ldfs.

Maybe. Maybe not. Depends on the rows involved, the join type, other filters, complexity of the query, data types and a few other things. Add indexes, see if they help.

Temp...

How are you trying to take a backup?

What's the exact errors?

Where did the .bak file come from?

That's fatal corruption you found there (system table damaged). Only solutions are restore from backup or, as you did, script export and recreate the database.

Have a look in Books Online, there should be both in there.

Please run the following (not the statement given previously) and post the full, complete and unedited output.

DBCC CHECKDB (<Database Name>) WITH NO_INFOMSGS, ALL_ERRORMSGS

Do you have a clean backup? (a backup...

If it's a system process (which are not necessarily under session id 50), then wait or restart SQL. Probably something like the checkpoint that can just be left to finish.

Post the code.

You might want to do some reading on SQL's permissions...

GRANT VIEW DEFINITION TO <database user>