Hoover Nextra won't start - door catch or interlock?

We've just been given this machine as a replacement through Freecycle - the door catch is broken but will open if you use a screwdriver or knife :) but I am wondering if the interlock might be broken as well as the "Stop" light is flashing and the "Door locked" light wont come on? (The previous owners said that they could get it to register as "locked" by repeatedly slamming the door.) Do you think it could be the broken door catch which is at fault or do you think we might need to replace both bits? Many thanks for any help offered.