Maybe the cord to the foot pedal has a fray in it? or it could have been kinked someway? My sisters machine did that. she got a new foot pedal and its working fine now. You might see if your repair shop has an extra pedal they will let you borrow to see if that is the problem. Hope it keeps on sewing for you now..my machine knows I can have a potty mouth when it acts up..when I finish sewing I always thank my machine for being nice to me *L* give it a pat on the head then shut it off so it can rest...
Happy Stitchin' Linda B.