boat sunk...why? should i sell?

[captainpond]

I have a beautifull 74 CC that had a 150 hp mer optimax. But it sunk in the slip last month. engine has seized. NO one can tell me why! Not even the owner of the marina. My boat was fine in the water for 4 weeks, and had a brand new bilge and floater put in with two new batteries running off a dual switch. Can anyone help me? I cant believe this.