Bipod does not work at all anymore

In BF3 on PC I remember using bipods early on, but since about december/januari they simply don't work at all anymore. The animation is not there and neither is the effect (I'm spraying all over the place with the machine guns).

I tried switching on and off the bipods on all kinds of guns. None work.

I tried picking up a kit from someone I saw using a bipod... nothing.

I know I need a flat surface, but even when I'm flat on the ground.

Is there a setting that could cause this? A bug? Do I need to reinstall BF3 completely?

One of the patches released earlier this year added the option to bind Deploy Bipod to a separate key than zoom. I'd venture a guess that this command is either unbound or bound to a key that you're not aware of. Try changing the key for Deploy Bipod in the Key Bindings Menu and see if that fixes the problem.