Did you check the belt ? It could be that the belt is all stretched out and the brush roller isn't turning...
If that isn't it, then go with something besides a Dirt Devil...It's just about the cheapest made vac out there...
I have a Dirt Devil upright. I took it apart and cleaned it all out because it wasn't picking up well, put it together, and no suction. Bags in properly, why could this be happening?