Where are my videos? Some of them are gone after I changed plans.

They're locked, not gone. On Free they're saved for 90 days; after 90 days on Free, videos past the limit are removed for good. When a plan has a lower video limit (Free has 5, Starter has 50), the videos past the limit are locked. The ones on your wall and your starred videos stay open first, then the newest. To open the locked ones: 1. Upgrade from the plans window, or 2. Delete videos you don't need. Each one you delete makes room for a locked video to come back. Each video goes back to where it was (for example, on the wall) when it's unlocked. Written reviews have no limit and are never locked.