Not picking up dirt - Bissell 6594 PowerForce Bagless Upright Vacuum

If the belt is over a year old replace it. Belts lose elasticity and will still spin but not clean the carpet.

The best way to pick up dirt with an upright vacuum is forward.

How to Fix a Vacuum That Lost Suction - Quick and Dirty Tips

www.quickanddirtytips.com/.../how-to-fix-a-vacuum-that-lost-suction

Oct 3, 2013 - It's true, a vacuum that doesn't have suction is not very useful ... The first and most basic reason a vacuum isn't picking things up off the floor is if the ...The lower your carpet, the closer the dial or lever should be to the bare floor setting. ....it off and shaking the dust off put the power right back in my vacuum!

Common Vacuum Issues - and what you can do to solve them

blog.mchardyvac.com/.../common-vacuum-complaints-what-you-can-do...

Oct 4, 2013 - Your vacuum's job is to pick up dirt, dust and debris - so when it stopsdoing ... Often when your machine is not picking up it is due to loss of suction. If yourvacuum cleaner turns on but won't pick up on carpet or bare floors, ...

Is your vacuum cleaner not picking up dirt and debris ...

https://www.mrright.in/.../is-your-vacuum-cleaner-not-picking-up-dirt-a...

Jan 7, 2015 - But many times it does not pick up or suck the dust as effectively as it is supposed to do. ... If the vacuum cleaner fails to pick up dirt and debris and has no ... Deep clean your expensive carpets to restore their original look.

clean the filter?

I have a Dyson and was having a similar problem some time back. I found out these bagless systems still have a filter that picks up the fine dust to keep it contained. Find out where yours is located and beat the dust out of it really good or just replace it.
Hope this helps.

sounds like you need to change bag and clean out hose and dirt channel underneatch behind brushroll.

Was it picking up dirt before?
If so then perhaps the suction hose has a buildup of dirt/fluff somewhere along it. If a large piece of material went up the hose it often sticks and small bits gather around it to cause a complete blockage. Can you take the hose off and check? Or shine a torch down?

It's probably not picking up because the belt is worn and stretched. With a new belt it will pick up a lot better. Here is the belts you need:

Dirt Devil FeatherLite Belt

There is probably a second or third filter (besides the canister) that needs to be cleaned.
I doubt that it's rotating the wrong direction.

There is a Clog in the machine...
Somewhere between the motor and the bag.
When you use the machine, the dirt picked up by the roller has no place to go but backwards.
You will need to disassemble it and look for the clog.