First thing, go to OPTIONS | DISK tab and Clear Unused Cache Files. If no help, open Windows Control Panel | Programs and Features and uninstall Videopad. Be sure that you Save Project AS first, giving it a unique name and #, so as to not overwrite earlier saves. Save Project (no AS) will overwrite.
Install the latest. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest. Retain your old install file and registration info.
Confirm that the PC video driver and Direct-X are up to date.
AMD / ATI users: http://support.amd.com/us/gpudownload/Pages/index.aspx
Intel users: https://downloadcenter.intel.com/default.aspx
nVidia users: http://www.nvidia.com/Download/index.aspx?lang=en-us
Update DirectX: http://support.microsoft.com/kb/179113
If problems persists, post again.