Small Engines (Lawn Mowers, etc.): tusqavania riding lawn miwer

Question
QUESTION: We just installed a new drive belt ordered through Lowes.  Now its loose and will not engage and move the lawn mower.  What could be the problem.  Thankyou

ANSWER: Did you measure the old belt against the new belt to make sure the belt is the correct length?

Did you make sure the belt routing is correct?  

Is the mower an automatic mower or do you have a 5 speed mower?

Eric

---------- FOLLOW-UP ----------

QUESTION: That did not answer the question.  Yes all of that was done and checked...   What engages the belt.  Its not engaging causing the belt made for the lawn mower seem to big.  Unless they numbered the belt wrong its the right belt.  But it will not propel the lawn mower.  Very odd.  Was just working.  Were thinking a piece by the transmission must be missing somehow.  Not allowing the motor to engage.  Thankyou.

Answer
If you have a hydrostatic drive an idler pulley spring keeps the belt tight.  The spring is connected to an idler pulley arm and pulls on the arm to keep the belt at the proper tension.

If you have a 5 speed model it will have the same setup, idler pulley, arm and spring.  Only difference is the belt tension is removed when you foot pushes the clutch pedal.

If the belt is the correct part number but seems to big then either the routing is wrong or the spring that pulls on the idler arm is dis-connected or broke.

I need the mower model number to look up your specific drive system.

Eric