New Walther Parrus won’t Cock / engage sear

As mentioned above, one reason for that to happen would be a trigger set too light. If you do adjust the trigger to finally catch the sear on cocking, be real careful if it's still in the "hair trigger" category. If that's your preference, be absolutely sure to hold on to the barrel when cocking it and putting that pellet in the breech. It would only be a matter of time when it decides to slam shut on it's own. The results can range from a squashed finger to a broken stock, bent barrel and more.