What version is being used? Look at the bottom-left of the Videopad window. Try 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 is required in order to register the newest. Retain your old install file and registration info. If there's an issue, you can always revert.
There's no toggle.
If a project has multiple video tracks, then the ribbon normally turns violet 
after individual tracks are cached (green lines 
complete). If it stays violet when small changes are made it's possible that the sequence has cached so quickly that you weren't aware of it.
Click on the Sequence in the bin (top-left) and that ribbon will be gray when fully cached.