Name of the movie with time paradox?

Ive seen a movie there was a time machine and ppl used it to travel in time and kill a t-rex over and over again and 1 time something went wrong and their weapons broke and the customer killed some bug and that caused a time paradox and the future started changing and one guy went in to the past and prevented all that from happening. Another scene i remember they were in subway and it was flooded and i think there was some monster there... anyone seen this movie?