You should replace the volume knob. Replace the knob using the Volume Knob Replacement guide.

The record player wont read the disc either because of the record it self or the needle/ cartridge needs to be replaced. First, try a few records and see if they all play or not. If they do, your all set but if they don't then you need to replace the needle. Following Needle/Cartridge Replacement will allow you to replace it

The most likely cause of the problem is that the motor is broken, preventing the rotation of the platter. In order, to fix the issue double check to see if the platter itself is damaged or broken. If, so replace that; in addition if it is not just the platter, go into the device and replace the motor. The attached guide for the Turntable Platter should assist in guiding you through the whole process found here JTA-230 Turntable Platter Guide