Vive heatset goes Black screen

[chunhinau]

I'm setting a new room scale HTC vive for my new office, and we need to use a 15M HDMI to connect the base station and the computer. I've used a 2.0 HDMI cable, all cables are connected well and the headset has a green light on, but there is nothing shown in the headset, it was all black, but when I turn on the mirror monitor, it works well and also can be shown in the computer monitor. 
I have tried many solutions and changed different cables still can't work. And when I changed a shorter HDMI cable it works. 
And the HTC live chat didn't reply to me
It there any solution??? 

[Synthesis]

 

 

15 meters is a long way to try to send a signal with that much data. Unfortunately, Vive was never intended for such a lengthy cable. You may have to use a shorter one. If that length is necessary, a powered HDMI cable might work, but we don't recommend using that with Vive.

 

Thank you,

-John C