Ive got the same problem. I got a 5 inch proformax vise for christmas.
Just went to use it the other day for the first time and it broke just triing to open the jaws. Now menards wont even give me in store credit. Thougth tool shop was garbage this performax takes the cake.
They have discontinued the vise so they wont exchange either. And they tell you to go screw yourself if you dont have a receipt.
Reason of review: Bad quality.