Hello, and welcome to the Forum.
Power for the wirefeed motor, and for the on/off controls ( probably a large relay or contactor ) is provided by an auxiliary power supply, which will be a transformer with 24v output plus a rectifier to DC. This section is OK, but there must be a fault in the main welding circuit. Have you tried to weld at all positions of the power selector switch?
With the machine powered off and unplugged, open the covers and start by checking for loose, corroded or burnt connections. On the primary side there may be push-on tags or screw terminals. The high-current secondary side of the transformer, rectifier, and inductor will probably have large bolted connections. These may look OK, but can be corroded inside, especially if the wires are aluminium. Check the joints at each end of the work return cable and the workpiece clamp.
Power for the main welding transformer may be switched by a contactor, and this in turn may be enabled by a small relay on the printed circuit board, which activates when the torch trigger is pressed. If you operate the welder with the covers removed, you may see or hear these relays moving. The main contactor may have a manual operation button. If so, carefully push this button with an insulated tool, and check if you can strike an arc.
The next step would be to check for a low-voltage AC output at the secondary of the main transformer, and the corresponding DC output from the rectifier. These voltages should range from about 15 to 30 volts, increasing in steps as you move up the power selector switch.