just got a training at work on this very situation.
basically, all the probiotics are "dead" now. they will still help you a little, so don't throw it away, but will not be as effective as living probiotics. the dead probiotics do have some benefits such as helping you digest your meal etc etc.
but since they are dead they cannot colonize and form a community in your gut. if you have just started taking probiotics i would recommend nature's way rueteri pearls. they don't require refrigeration and it is the best probiotic to start with. it is actually a probiotic only found in breastmilk, so it is VERY important to the tribes in your gut!
it is critical to keep probiotics that need refrigeration cold because this keeps the live cultures dormant. allowing them to even reach room temperatures activates the cultures and theyt start to grow. if they have nothing to feed on, they will die.