If the lid cannot be pressed down upon then the valve may be assembled incorrectly. Here’s some guidelines to help:
To re-assemble your cup simply turn the screw ring upside down, placing the silicone disk inside with the grooves facing up. Next, take the lid top, pushing it up through the hole in the silicone disk aligning the locking connector. Then twist to lock. Place the lid on the base remembering to align the two dots on the back.