If you can feel the air exhaust from the back it means that the motor fan is actually moving air - which is good - all you have to do is discover where the air is getting in?
If you can't feel air (or much air) and the motor is running at a higher speed and higher pitch it means that not enough air is getting in due to a blockage of some sort.
Sometimes a split in a hose will cause a loss of suction.
It's a pretty simple system - a fan draws in air and blows it out again - filters and a bag trap the dust particles - the moving air is used to cool the motor.
Try tests if you can without the hose and even without the bag (if the machine allows this) - cover the inlet hole with your hand to check the suction.
Peccavi, July 2009
