Machine w/not squirt

Inspect where the suction comes the machine into the water tank and through the tank to the nozzle assembly. If something isn't seated correctly or isn't working properly it could cause a suction loss.

You already said it, so check the carbon brushes. Once it is no longer able to push the rotor or stator it need to be replace. Carbon brushes are customized at the machine shop, so you should bring it so that you have a sample of the brushes itself. Just be observant when disassembling the motor so that you put it back to exact place.
Thanks for asking.

First check the motor duct gasket. The motor duct gasket is visible once the tank is removed. It is located underneath the handle on the top of the base of the machine. It has a black rubber coating around it. If there is no suction there please let us know. If your machine does have suction at the duct, continue to check the following:

- Ensure the Ready Tools Dial is set to the appropriate setting (Floor Cleaning or Hose Attachments).
- Remove the tank from the machine and ensure the tank lid is attached properly. The front window must first hook onto the lip of the bottom of the tank and then drape over the tank. Latch the bottom tank to the top tank lid. THIS LID CANNOT BE ATTACHED PROPERLY IF THE TANK IS NOT REMOVED FROM THE MACHINE.
- Make sure the Water Tank is not full on the outside of the bladder. If it is, empty the tank.
- Ensure the hose is firmly attached to the back of the machine. If not, re-insert as necessary by twisting into place.
- The machine must be in an upright, locked position and set to the Hose Attachment setting. If the handle is slightly tilted back while using, it will create a small gap at the suction inlet (where handle meets gasket, above the Bottom Tank) which will cause little or no suction.
- Check the red Tank Lint Screen for debris. If the Lint Screen is dirty, the unit will have poor suction. Clean the Lint Screen if necessary.
- If the float flap door in the tank lid is activating prematurely when you turn the machine on, this flap door should be replaced. This tank may need to be emptied.
- Check the Tank Lid and Tank for damage.

That means that you need to replace the pump belt. Here is the belt you need and a manual you can view:

Bissell 7901 Belt and Manual

The cleaner goes into the small bottom at the very rear of the machine. It is uses full strenght (don't add any water to it). You add clean water into the bottom clear plastic section on the front of the machine. The clean water bladder is soft plastic and it is filled from the top. When you start using the machine, the dirty water will get suctioned into the section surrounding this bladder. The machine will stop working when either the bladder is empty or the dirty water section is full. Remove the entire plastic section to dump out the dirty water.

I forgot how to start my Bissell Pro Heat Upright Wet/Dry Please advise

I took apart the cleaner to clean the parts that were dirty and I can't seem to put the roller back in. Any suggestions

You are supposed to buy the Bissell soap. On the bottle depending which cleaner you need. The directions are on the bottle. Please do not use house hold cleaners because you can cause serious damage to the vacuum.
Go here, this pg. shows the 7901-1 click the user guide pdf & print the instruction if you choose:
http://www.bissell.com/Bottom_Menu/Product_Search.aspx?Criteria=7901-1+ProHeat+
Good cleaning!
Please vote..........

Does water squirt out of the hose nozzle, if it does, then check the heater inside the handle asm. Make sure that where the tubes hook up to it are not clogged. If water doesn't squirt, check for the seal at the bottom of the tank, it needs to be on the tank, not in the hole. The flow indictor cap is leaking air or maybe is too tight. If you had the top cover off, make sure that the tubes are routed right so as not to get pinched when the cover is put back on, the smart mix knob should be in the water setting and that the piston is on the bottom of the smart mix know. Pump is bad.

Does water squirt out of the hose nozzle, if it does, then check the heater inside the handle asm. Make sure that where the tubes hook up to it are not clogged. If water doesn't squirt, check for the seal at the bottom of the tank, it needs to be on the tank, not in the hole. The flow indictor cap is leaking air or maybe is too tight. If you had the top cover off, make sure that the tubes are routed right so as not to get pinched when the cover is put back on, the smart mix knob should be in the water setting and that the piston is on the bottom of the smart mix know. Pump is bad.