Sorry to hear you're having an issue.
You might try calling your cable company to see if they can reset the box, or if there is a firmware update available for it. The picture going out - and not the audio - sounds like it may be a HDCP (copy protection) issue, which can be pretty common with cable/sat boxes on the market.
I don't know if it will solve your problem, but might be a good start.
My components are as listed:
Motorola DCT6412 III - Comcast digital cable
Samsung LN46B640 46" LCD-TV
I have a HDMI cable from the cable box to the receiver and then out to the HDMI1 port on the TV.
The problem is sometimes the video signal to the tv is lost for a second, yet the sound is unbroken, so it appears its the link from the receiver to the TV. I also have a DVD player hooked up via HDMI through the receiver yet i have never noticed this issue while watching DVDs. It doesnt seem to happen to often nor on a pattern. Anyone else have this problem and what might be the cause? Again it is very infrequent and only last a split second but is still anoying.