Yes Kathy, it can go bad. You can tell by smell, if you know how good formula is supposed to smell (of the same brand). Check expiration date and I suggest tossing after that date, even if smells ok - unless it was kept in the freezer from the time you bought it till present and then you can keep somewhat longer.
I keep mine in freezer once opened and smell tested and only take out 1/2 or 1 pound at a time which I keep in an air tight sealed container in fridge or freezer. I use that 1 lb. up fairly quickly.