i thought it must be "the beast in the cellar" after reading a couple of reviews, but the description of the "beast" sounded more like rip van winkle which wouldn't have scared me in the least...i went the "st. elsewhere" approach and found "the unseen" which has the same family-secret-locked-in-the-basement theme and since it's from 1981 and apparently the "unseen" was given a good makeup job, this is probably it...

thanks for the help...