Is this a 5 blade fan? If yes, it's probably a faulty capacitor. I was told that the replacement would cost around $50. I bought my own capacitor at $18 @ Jalan Besar and replaced it myself. Warning: Only do your own repair if your know what you're doing.
Judging from flush alone can't really tell. If you open the tank, you can try flushing it and see how much water drains out. Seen mine drain 1/2 tank for 'small' flush, 4/5 tank for 'big' flush. Quite obvious.