I'd check your HDMI cables first. You should be using Certified High Speed HDMI cables from someone like Monoprice, MediaBridge, BlueJeans, etc. If the cables are fine on your used plasma (works ok on another tv for example) then "used" may be your problem. You may have to get a calibration disk like the free AVS HD709 disk and set the basics (brightness, contrast, sharpness, aspect, and color). And plasma tv's don't usually do very good in bright rooms but that's probably not your issue.