I'm 36 and remember this movie from when I was a kid during the late seventies/early eighties. I thought it was a Disney movie but I couldn't find it. It has a really long title and is something like, "the fantastic world of professor..............." or something along those lines (with someone's crazy name). There is a weird little kid (maybe w/ a beanie hat) that ends up in this strange dreamworld with magical made-up musical instruments and a mean music teacher, world ruler, or something that won't let him leave. I remember him running around, trying to hide, and discovering all these strange, trippy things related to music. It's driving me crazy. Please help!

You may be thinking of the 5 thousand fingers of Dr. T. It was a movie about a kid who doesn't like his piano teacher and ends up having this dream about this teacher who creates this huge piano and enslaves children and forces them to play this huge piano.
In the dream his mother is under the spell of the Dr.

Is that the one your thinking of.

wintermoon