I also have NVIDIA GeForce GTS 450 graphics card.
What version of Premiere Elements are you running on your Windows 7 64 bit computer?
Is your video card driver up to date according to the web site of the manufacturer of the video card? What video card does your computer have? If the video card driver is up to date as described, then delete the BadDrivers.txt file found in the path:
Local Disc C
and in the Premiere Elements Folder is the BadDrivers.txt file for 12 that is probably sitting there among folders. You do not want anything in those folders in the Premiere Elements Folder that I have directed you to. Make sure you are working with Folder Option Show Hidden Files, Folders, and Drives active so that you can see the complete path.
What are the properties of the source media that you are putting on your Premiere Elements Timeline? And, what project preset did you or the program set to match those properties?
Am I correct in that this is an issue where "it worked before but not now'?
Do you have the latest version of QuickTime installed on this computer with Premiere Elements?
Are you running the program as Run As Administrator or from a User Account with Administrative Privileges?
Consider uninstalling Lightroom 5 until you work through the Premiere Elements problem.
We will be watching for further developments.
I did not see your latest post until after I had posted mine.
Did you recently update the NVIDIA video card driver? If so, try rolling it back as part of the troubleshooting.
Rolled back to GeForce 320.49 Driver and it helped, all later updates did not work! Thnak you so much for excellent support, you made my day!!
Great great news. At moments like this I cannot put enough greats in there.
Very pleased that you are able to move forward with your Premiere Elements 10 (with NVIDIA video card) projects.