I have a 40 year old Singer machine (portable not treadle) and hadn't used it for about 8 years - when I tried threading it the top thread would not take up the thread from the bobbin underneath. We tried everything , in the end I contacted a retired sewing machine repairer who told me exactly what it was. Apparently there is a little rubber belt inside which perishes if not used for some time. It was easily fixed, replaced this belt and gave machine a good overhaul and it works perfectly again - £38, can't be bad for these days! maybe you have a fault similar to this, worth looking in yellow pages. Hope this helps.