Subwoofer problem

Help!

I have problem with my B&W ASW 800 subwoofer with Rotel RSP1068. Just started not working. Both of them are brand new.

Just want to try more before I bring it to place where I bought since subwoofer is so heavy.

When I do the speark Test Tone from Rotel 1068 processor, there is no sounds in subwoofer, all other 5 speakers are fine.

But when I switched off the subwoofer for a while then turn back on it, hear a sound for a second then nothing. However not everytime I turned it off/on again, just sometimes it works momentariy but not always. so I think it's not the cable I think. Also I see green light at the backside so power is o.k.

Thse are my subwoofer settings,
Volume:12 o'clock position.
Mode: ON
Phase switch: 0
Low-pass filter: OUT
Low-pass frequency: irrelevant(use for home theater) but I set it somewhere between 80~100hz

Rotel RSP1068 processor settings,
Speaker setup: small to all (Front, Center, Rear)
subwoofer: Yes
leave dB as 0 (default)

So Can you tell me what I can do to diagonosis?

I'll really appreciate any feedback.

Thanks.