Sometimes she will tell you what you did that was "wrong", wrong enough to provoke days of silence, and it may be something minor: You talked about something menial to her important friend at a party. You played with your salad. You put too much Parmesan cheese on the pasta. Or he got a good look at your thighs and you are developing cellulite.
Is it an intentional punishment? Maybe, maybe not. The partner may really be "splitting" you, common in those with borderline personality disorder. He/she actually doesn't regard you. You don't exist to him or her.
If you've experienced this kind of treatment, if you don't know how to handle it, join the discussions at BPDfamily.com. There's an ongoing Workshop on the Silent Treatment in which you can participate right now.
You aren't alone with this form of abuse. Others have experienced it also. And they may be able to help you deal with it.