Your reciever could be shorting out somewhere. You may have something briding your positive and negative connections.
My first sub box i ever had was a prefabbed one, and when i used the connection box on the side, it would cut out the amp. Wired up directly to the sub, it was fine. So slapped a new box in the side and went on.
Your amp is crossing somewhere. could be internally, on the posts, inside the cable.
Try new cables, different speakers, etc. If swapping does nothing, you'r amp section may be fried.