My Viore 42" LCD HDTV's HDMI inputs currently make the TV's picture signal intermittent when reading a signal from my comcast cable box and a few functions of my PS3. How can I fix this?

check hdmi cables first then its the box going bad.

not sure if this link will help you out but have a look. Toshiba Regza 42 Black Screen Google Search

Are you using the HDMI for the Tivo and the Comcast box? If you do, then you need to verify that the HDMI sound set up at the boxes and at the TV are set to send and use the audio through the HDMI ports, not through the analog ports since HDMI allows you to use either analog audio or Digital audio through HDMI cable, you have to choose.
Please read the Tivo, Comcast box, TV setup for details.

Basic troubleshooting guide here:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r7406380-tv_training_manuals
Failed TV and Monitors pictures: http://s807.photobucket.com/albums/yy352/budm/
Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague
Parts: www.shopjimmy.com
Parts: www.interliquidparts.com
Capacitors kit: http://lcdalternatives.auctivacommerce.com/Default.aspx he can make you a set of caps.
Or www.digikey.com just make sure to use caps with low ESR, 105c, high ripple current, long life rating such as PANASONIC FM or FC series.

there should be other inputs like S-Video or HDMI. To convert the signal-go to E-BAY and type in "RCA to HDMI"(for example). Got my converter cable there for $5.00 while RADIO SHACK wanted $30.00!

I'm thinking the Comcast DVR box maybe putting out weird HDMI signals and the TV can't translate it. I would call the Comcast people on this one.
In the meantime, I would try finding another source the uses a HDMI cable to rule out the TV as the problem. Basically, testing the TV to see if the problem still happens when you use something else than the Comcast box. Try a Blueray player, Playstation 3, or Xbox. Just something that uses a HDMI cable.

TV was on, screen went black... Stanley cup playoffs double OT continued sound only. TV now just clicks on and off. 

The TV will not display closed caption with HDMI input. It must either over-the-air (antenna) or composite input for the TV to manage CC.

To get CC with HDMI from your Comcast DVR, you need to configure the cable box. Instructions can be found here:
http://en.wikibooks.org/wiki/How_to_use_a_Motorola_DVR/Setup

If you want CC all of the time, this works well. But since you must power-off the cable box to change the setting, switching CC on and off is a real pain.

Your set-up is similar to mine (Sharp Aquos 46" and Comcast DVR). I have the composite output from the cable box going to a DVD-recorder and on to the TV. Whenever I need CC (usually to catch some mumbled dialog), I just rewind the DVR, and switch the TV input to the composite input. Then I switch back to HDMI to continue watching in HD.

Connect the HDMI outputs on your various components to the HDMI inputs on your receiver. Connect the HDMI output on the receiver to the input on your TV. HDMI incorporates digital audio, so no need to buy optical audio cables. If your receiver does not have HDMI inputs for all your components, you will need to make a choice. HDMI = Best, component video + optical audio = second best, S-video+ optical audio = third best

Had the problem. Turned out to be a defective hdmi port circuit board.

My 42" Westinghouse HDMI inputs just stopped working. I thought it was the TW Explorer 4250HDC issue so I got a new one from TW. Still said no signal from HDMI. So, I shut the TV down and pulled the power cord out of the back. I waited a few seconds and reconnected the pwr cord. The TV "re-booted" so to say and now the HDMI inputs work. I think TVTEK has the right idea that it is firmware/software related. In the mean time, you might want to give that a try.