2001 VW Beetle - Lock Problem
 

So this morning, I wake up only to find out my key doesn't work.
When trying to unlock it from the outside, instead of pushing back into it's normal position, it'll just stick, and when turning it, it makes a sort of soft grinding sound.
After playing around with it for a little bit (10 min. or so), it finally manages to unlock. (And then refuses to lock)

Also note, I purchased the car (used) from a private party, and they only had the valet key to give me.

Any suggestions on what to do, or at least any speculations on the problem would be greatly welcomed!