Distributor on a Econoline 150

I have a 1993 Ford Econoline150 van with 199,956.00 miles. I have been hearing a high pitched squeal off and on and now it won't start. I took it to a mechanic and he says it is my distributor. but he can not get it off. why would he not be able to get the distributor off? Help me please. I need this vehicle back on the road as soon as possible. Thank you in advance for your help!