Check the dirt container level. If it is not full observe the spinning action of the debris in the container. If this appears reduced, check the suction at the hose by holding the palm of your hand over the end of the nozzle. If the suction is poor and the high pitch noise does not reduce when removing your palm. Check for obstruction in the hose. The procedure is outlined on pg. 12 - 13 of your user guide. If you no longer have your user guide a PDF version can be found at,
http://www.bissell.com/WorkArea/DownloadAsset.aspx?id=8590011715
Your unit is equipped with a thermal cut-off switch to prevent damage to the motor from overheating. If your unit turns off, or won't power up, try letting it sit for 30 mins to cool down allowing the thermal switch to reset. If there is an obstruction preventing the brush from turning, the unit may turn off. Unplug the unit and remove any visible obstruction from the roller by reclining the unit, turning it over, face flat and carefully cut away any debris, hair, string, etc. which may be preventing the brush from turning. The brush will automatically reset itself when the unit is plugged back into an outlet. If not it is possible the brush assembly may have locked up.
Follow these steps listed above along with any general filter maintenance to see if this solves the problem. If not, let me know and we can take it from there.
Thanks and good luck.