Sounds like your carbon brushes may be breaking down, or the thermal cutout is bad.
Unless your filters havent been checked/changed since eternity. Does it stop overheating if you take out both filters and turn it on? If not, you'll probably need to get the motor out to have a look at it. Does it sound ok for the brief time it runs? Does it sound different with the cyclone unit off vs on? Does it sound different with the cyclone on, but the filters in/out too?
There's a few guides on where the filters are and how to get the motor out on them on the main forum!