USB 2.0 Tv Box Won't start up!

i recently purchased a usb 2.0 tv box, and it worked great at first, but now, most of the time when i start the program, a blank screen pops up. the power light on the tuner is not on, but the computer still detects it. usually a picture pops up when there is no signal, but it wont even turn on! any suggestions?
os:windows xp sp2