I cannot even imagine what your mechanic could have possibly done while replacing a screw on the M/C to cause it to fail completely. I would first start by confronting the mechanic with WTF he did to your bike (but that’s just me ). Other than that more info is needed. Do you have any pressure at all? The lever just moves freely (w/o any resistance), or not at all? When you bled did any fluid come out when you squeezed?