S3 frozen - now what?

In the past few months I have replaced my S3's hard drive with one from WeaKnees, and replaced its power supply with one from WeaKnees. The box worked for a few weeks, but now it has a new problem. It displays a single frame from a live TV show and won't move off it. None of the remote or front-panel buttons cause any response. And all the front-panel lights are off - even the clock is gone.

Does anyone know what's happening here, and what I need to do to get the box working again?

Thanks.