It’s verrrry difficult to copyright a short chord progression, say, of four chords or thereabouts. In fact it’s impossible. Having a music composing mental block? Go find a chord progression from your favourite piece of music (if you have a crisis of conscience about being ‘inspired’ in this way, firstly don’t, Bach did it, but if you’re STILL feeling guilty, turn it back to front, jiggle it around first), play a little melody over the top and then, ta-da! Use all of that as a basis for your theme.
For example, why not use I-V-vi-IV, as illustrated in this little YouTube video. Evidently, you won’t be the first 😉