What causes my Shark Vacuum to work only intermittently?

\015 I have Shark Vacuum that works great some days and not at all on others. The usual suspect is hair(which is easy enough to cut out), but is not always the cause.Usually one of 2 issues arises: (1) The rotating brush does not rotate (2) The vacuum does not pick anything up, just blows things around.When I tilt the handle back the brush is supposed to rotate and a green light turns on. Sometimes the light will not turn on or will turn red if the brush won't spin. Usually this issue happens on carpet. A few days later I might turn it on to the same issue, or to a fully functional vacuum.Yesterday, my problem was No. 2, it stopped picking up items (on tile, worked OK on carpet). Items simply blew around on the floor. I tried disconnecting the hose to suck them up, but it didn't have enough suction to collect the items.I don't want to invest in a new vacuum because I know this one is great when it works, but I need to master it when it doesn't.What might be causing the issues and how can I resolve them?\015 – Shark Navigator Bagless Upright Vacuum