Database transaction log is full - Simple Mode

Growth is either down to 2 reasons:
1 NO DISK SPACE
2 LDF Autogrowth restriction has been reached

First thing I would do is Change Recovery from FULL to SIMPLE if not done so already

http://knowledgebase.solarwinds.com/kb/questions/1359/Changing+Recovery+Model+of+database+back+to+Simple

.LDF file grows out of control, How to recover:
1.) Make sure recovery model is set for simple and not full
2.) Backup the database, this will mark the data in the transaction logs as committed and no longer necessary.
3.) Shrink the database again to reclaim the log space.

How to: Shrink a Database (SQL Server Management Studio)

How to: Shrink a File (SQL Server Management Studio)

1. 4.) If above doesn’t work as last resort is to detach the database (do not force it to detach if it gives an error that it can not detach, this will damage the database)
   once detached delete the .LDF file and reattach the database.
2. 4.) Stop Orion Services.
   5.) In the SQL Mgt Studio or Orion Database Manger, right-click on the NetPerfMon database and choose "Detach".
   6.) Navigate to that directory where the MDF and the LDF files are stored, and delete ONLY the LDF file.
   7.) Go back into the database manager, right-click on your SQL server, and choose "Attach Database."

        8.) Select the MDF file, and hit okay.

         9) Remove the LDF file entry hit OK
    

It will recreate will 0KB LDF File automatically.

Future Proof so it doesn’t recoccur
After above all should be fine, but have you check LDF File growth doesnt reoccur.

Also once set to SIMPLE Recovery, LDF file should never really be over 1GB if all running smoothly.
But can also configure LDF to Restricted Growth, so say LDF File on Drive over 100GB Free,

  You could restrict LDF to few dozen GB just to be safe,
in case LDF growth reoccurred and LDF goes 100GB and brings down server due lack disk space.