Okay thank you.
Based on the fact that you said the Cable Box first lost picture, then also that the DVD player lost picture, this indicates a problem with the TV itself that cannot be corrected via any settings or adjustments.
The TV needs a software update to fix the problem. The TV's mainboard runs on software that allows it to produce the video image from external devices, and when you have the problems you've had with the set, it means the software is corrupt and needs to be updated.
If you're looking to perform this update yourself, the link below is to Mitsubishi's support page, and has instructions on how to perform the download (you will need a USB drive to download the software onto), and also the update. You will need the most current version fo the firmware to fix this problem.
If you are not comfortable performing this type of repair yourself, then you would need to use the same link to locate an Authorized Mitsubishi repair center to update the TV for you.
I wish I had a quick fix for you on this problem tonight, but unfortunately the software does indeed need to be updated.
If you need further assistance let me know.
If you're satisfied with my service (not the problem that the TV is having), please do not forget to rate my service accordingly.