sogno 8800hd black screen

Hi there i'm hoping someone can help me. I tried to set something to record and my box froze. i had to unplug the box because none of the buttons would work. When i turned it back on the channell list still came up but the screen just stayed black and has not come back since. Please does anybody know how to fix this. The person I bought it from wont reply to me so I'm totally stuck.
Thanks in advance.