Belt thensen lose cause a baring came off

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

Vacuum belts lose elasticity and will slip. It may spin the brush roll ok when you look at it but be so loose that when. Vacuuming carpets the belt will stop turning. The motor shaft is still spinning and will melt the rubber belt causing a burned rubber smell. Belts on almost All vacuums need. To be changed at least twice per year.

sounds like your belt is worned out its not gripping i suggest change belt have it replaced

The brushroll might be restricted from turning freely causing the belt to slip on the motor shaft.

To put it simply, no. By floor mode I'm assuming you're stopping the brush roll from turning so that you can clean hard surface floors instead of carpet. When the brush roll doesn't turn you do lose agitation which vibrates the carpet so that the dirt is more easily picked up by the vacuum. But you don't lose suction because the brush is not turning.

Hello :
try this please : switch the carpet/bare floor dial back & forth 5 times, ending on carpet. Tilt the handle back as if to vacuum upright & lay the vacuum on its side so it is resting on the side opposite the carpet/bare floor dial. Turn the vacuum on.
or try this also if the above suggestion didn't work :
Maybe the belt is broke. You will have to replace the belt before the roller can spin. You must have run over something in the carpeting like string or whatever to have it break. Happens all the time. Get several replacement belts to keep as spares while you're at it as nothing is worse then having to vacuum and no spare belts.
please rate !

Yes belt probably broken. Also the brush roller heats up on the ends, causing the plastic end cap nearest the belt to melt/weld to the end. It's supposed to spin freely. Also 2 bearings inside tend to become sticky, probably from heat. Next thing you know, the brush roller is seized and will not turn. Probably the whole reason the belt breaks. New belt & new brush roller, 30-35 bucks. It will happen again. Now you've spent almost half what it costs new. Lose the junk. 2 years for a cheap vacuum is the normal life span anyhow.

I took the plate off and cleaned up the vacuum brush bar. Since the belt was not broke I knew that was not the problem. I know when the setting is bare floor, the brush bar will not rotate. That was not the problem. I just keep turning the knob from bare floor to carpet, several times. The setting must have been "off" just a bit because after several times turning it, it must have reset in the proper setting. The brush bar did start rotating just like normal.

Most likely your belt wore out and broke.
Here is a handy vacuum repair tutorial that should get you back cleaning.

Below is a short excerpt from the instructions. The link above will take you to the full version with images.
When your vacuum starts to lose cleaning power, requiring multiple passes to get an area clean, or the self-propulsion loses its zip, chances are you need to change the vacuum agitator belt. After only a few months of use, most vacuum belts stretch out enough to slip, causing the agitator to spin more slowly.
Replacing the belt is quick and inexpensive. New belts are available starting at about $5. Belts come in numerous brands and sizes, so bring the old one to the store for a guaranteed match.
Fifteen minutes, two screwdrivers and a new belt are all you’ll typically need to complete the job.

Stand vacuum up and with it plugged in. Rotate knob between carpet and bare floor and back 5 times leaving it on carpet when finished. Rotate vacuum back from upright position and lay vacuum on the floor, rotating it onto its side. Turn vacuum on.