Engine made low but roaring sound and now will hardly turn over, wont crank.

Vehichle sat idle for two months then had valve cover gaskets replaced. Engine ran well after, but with whooo sound from front of engine during acceleration. Drive belt replacement reduced the sound. Whooo sound stopped to be replaced by a sound like a pulley with bad ball bearings. Engine began faltering when slowing for stops while I was driving and went dead as I was returning home. There were no warning or check engine lights, oil pressure showed good and engine not overheated. I managed to crank it one time but it went dead within seconds. Though the battery is charged well the engine does not want to turn over, only very grudgingly for a few very slow turns, not fast enough for a start. Over the last year or so I added a pint of oil treatmeant twice. Have I caused my engine to seize or is there a (hopefully) better answer for my problem?