How can I get my MK808 mini Android PC to output to my TV?

I had [this mini pc](http://www.sainsmart.com/android-mini-pc/sainsmart-ss808-pc-on-a-stick-for-android-4-1-dual-core-1-6-ghz-a9-processor-1gb-ddr3-8gb-internal-storage-dual-wifi-module-on-board.html) from a friend. But I cannot power it up. When I connect it to TV with HDMI cable, the light is blue, but I got nothing show on the TV screen. I've tried some different HDMI cables, but it will not put a picture out to the TV. Can anyone suggest what the problem might be?