It was fine for about 3 years and tens of videos based on both DV and jpegs.
About 3 videos back the MONITOR window stopped working.
It won't update from timeline scene to scene. It also won't show video, although the sound runs ok.
Older projects do run OK and the monitor Window works Ok for them.
When I burn to DVD that's OK too,
I can't find ay settings I may have changed.
What computer operating system is involved?
Since you are working with Premiere Elements 10 and having the problems that you describe, the first question that needs to be is "What video card/graphics card does your computer use?" If the answer is NVIDIA GeForce with up to date driver version, please stop. That is likely your major issue. Please review
There the answer has been to roll back the driver version to May 2013, using older driver download from NVIDIA. Lately even that has not been proven possible since the older drivers offered there are not old enough. We need to factor Premiere Elements 10/NVIDIA Ge Force in or out before going on to other possible causes of your issues.
Your description suggests that in the past you might have been working with SD projects. Is that correct?
At the present time have you switched to HD workflows instead of SD workflows?
How do the properties of your source media differ when you compare the older projects that work now and the newer projects that do not?
Please review and consider and then we can decide what next based on the details of your reply.