Sewing machine woes

My sewing machine has gone wonky. I know almost nothing about how sewing machines work, so bear with me. It's been working just fine until it suddenly started misbehaving. It doesn't always feed correctly anymore when I first start sewing. It will just go up and down in the same spot forever, or until I make it move manually, and then it's fine. I thought it could be dirty and in need of a tune-up or whatever you say about sewing machines, so I took the bottom thing (technical term) apart as directed by the maintenance page of the manual and cleaned it all with the brush, and followed the instructions to clean and oil the squicky bits. (I have no earthly idea what squicky means. Sometimes my brain tunes out and my fingers substitute words.) No change for the better, although the stitches just completely knotted up on the back one time, so the opposite of progress. M changed the needle for me tonight, and it worked okay for a few minutes, but then the needle snapped. (I don't know if the problem was actually solved by anything he did or if it was coincidence.. it didn't happen every time.) Anyone have any idea what's wrong with it? I don't understand why it would behave differently all of a sudden, but I really need it to stop so I can get stuff done.. it's very frustrating, especially since I know so little about it.