Oreck vacuum blows air does not **** air. The bag

http://www.fixya.com/support/t10109120-oreck_vacuum_notRepair. Sometimes the belt on a vacuum cleaner eventually cracks or splits, causing the vacuum to lose suction, which can cause dirt to blow back out of the unit during use. To investigate, disconnect power and lower the cleaner head, then turn the vacuum cleaner over and remove the belt cover on the cleaning head._picking_up

Check for a clog in the base or in the handle tube.

All oreck uprights take bag type CC. I would Recommend buying oreck brand bags. they have the only patton on the bags. off brand bags will work but they will leak and tear and break.

It may have a clog in the unit. if you unzip the outer bag, the hard shell bag, the bag on the inside should inflate instantly as soon as you turn the vacuum on. if it doesnt then it has a clog. Halo's are on of the hardest vacuums to work on. they take a lot of time and is almost impossible to explain how to fix it. i would definitely recommend bringing it to an authorized Oreck dealer to fix it if it is not a clog.
also make sure your roller brush is spinning when your on your carpets. if it is not spinning then i would try the reset button while the vacuum is on which is on the right side of the back of the vacuum is a little red button on top. you cant miss it.

When you turn the motor on, the bag should inflate quickly and firmly. If the bag does not inflate, you probably have an obstruction in the handle tube. The tube can be disassembled to remove the plug.

This is a sign that the bag is full or there's a clog in the air flow piping. Check behind the brush for clogs and remove if there is. Open the cloth bag, remove the paper bag, and check inside the tube. If no blockage is visible, drop a coin or marble down the opening and see if it rolls out. If not, there's a clog that needs removed. You can use an air pressure hose to blow it out..

You need to remove the main head with the brushes from the front and install the safety cup. The remove the bag by unclipping from the top and disconnecting the boot end from the bottom with an outwards twist. Now attach the hose to the exposed outlet; attached the thin nozzel designed for inflating to the hose and switch on - you will feel air being expelled from the hose.
Air, which normally contains dirt and dust because you're hoovering is blown into the bag, but now with the bag removed; the air is blown into your hose, through the attachment and into what ever needs inflating.

For a good visual set of instructions click on the following link and scroll down to the second set of instructions :
How to change hoover to a blower

These units are called dirty air units because the dirt literraly runs thru the fan attached to the motor and is blown into the bag. Most newer vacuums are called clean air because the filter bag is in the path, and the dirt is sucked into the bag, never reaches the fan or motor.

I'd say if it is that dirty, may be a fire hazard, and you may have worn out the seals on the part down at base that pivots to a point that replacement is necessary.

(I'd blow out the dust and keep using if it was me, and then check again in a few weeks, before I replaced. But I like living dangerous.)

Follow the directions. With Oreck OEM bags they should attach easily. You need press the cardboard frame over the small nodules on the bag holder and they will stay in place

check for blockabe in bag inlet area, or bottom of unit by intake pivot.
ez check is to feel if bag blows firmly up with air when on, if not, you have a blockage.