Devil May Cry for PS2 acting weird?

So I was playing Devil May Cry (the first one) for PS2 the other day, and I was only on the 3rd level when it started randomly pausing every time I hit a button. It wasn't even the pause button I was hitting, it was circle and square. I bought it as a used game, by the way, so could that have something to do with it? Or maybe my controller? Has this happened to anyone else?