Most blender / mixers have one safety switch per jug.
If your BBL300 has one jug then it should have one small switch where the jug's locking tabs will lock the jug into position.
This is usually visible as a small plastic piece (may be black in color) just under an L-shaped groove on the base.
This is a "Normally-Open" switch, so that only something pressing the switch lever will switch it on.
No jug no work. You need jug.
You can test the spindle & motor by switching on (low speed) then use a flat plastic tool (eg a plastic spoon handle) to press this switch tab in.
If it starts, motor is good, then you can buy a jug to fit.