It wont start

You have lost 1st gear. The gearbox will require dismantling and replacement of the 1st gear part (diving key) if they are still avaliable. I wouldrecommend contacting yout local hobart call center and speaking to their technical team about the age and probability of parts

call in an electrician as it may be the start/run capacitor for the motor ( indicated by motor humming but not running)
the gearing will make it very difficult to turn the blades by hand as the motor will be spinning at either 1400 rpms or 2400 rpms down to around 50 rpms for the blades

if i t whont start brig it to a repare shop or try to spin the shap thing then start it

Check for broken wire under back cover. Check operation of switch contacts on black speed control plate. Check carbon brushed under black screw caps on the sides. The brushes are keyed, they only work one way.

You probably need a new switch AND motor brushes.

My fantastic guy just rebuilt my A200. He says it's likely that your back plate is slightly off center so that the center arbor is touching the windings-- any contact and the machine won't run. The tolerances are thousandths of an inch in there.

First, does the housing for the beaters spin when the beaters are not in place? If so, then there may have been a stripping of the cogs in the housing. If this the case, you definitely need to buy a new mixer. If the housing for the beaters does NOT spin period, then there is no question that you do need to buy another mixer.

The answer is clearly in the starting circuit which doesn't have too many parts, but depends on the type of starting circuit your mixer uses (electronic or mechanical start switch). I'm assuming your mixer isn't very old, as the old units used brushed motors which did not have starting circuits.

The parts of the starting circuit are the motor start winding, the start capacitor and the start switch (probably electronic in your case which is a small silver box with four wire terminals on it). The capacitor should be tested with a multimeter after verifying it's not holding a charge (check with multimeter set to DC Volts, mixer unplugged, should read zero volts).
Start winding should be tested with the meter to measure ohms. Locate the wires leading to the motor (hopefully only three wires) and you should get a reading for all three combinations of measurements (wire 1-to-wire 2, 2-to-3, 1-to-3) if meter indicates open on any of these, motor stator is bad(this is pretty rare and quite expensive).
Electronic start switches are not very simple to test, but if the capacitor and motor test out OK with the meter, and all the wiring is intact (look closely for loose wires, burned wires, poorly crimped terminals, etc.) then it must be the start switch.

take off the side cover where gear shifter is, you probably have the original arrow hart contactor in there ,that part is obsolete but you can get a kit from hobart to upgrade the control circuit

Motor start capacitor failed or start run switch mounted at back of motor housing damaged