Stepper engine problem?

I have converted a Proxxon MF70 to CNC. When the engines are not connected to the machine every thing is working fine but once connected the engines aren't able to move, they just shake.

I'm using 23H1404 steppers and a 24V 15A power supply.

I believed that for such a small machine this would be sufficient. Must I change the engines for same whit more torque?

Thanks