I am assuming that your stove and oven are both electric. If the top cooking elements heat properly, you have electrical power to the stove. Find the fuse, circuit breaker or "reset" button and verify the fuse is not blown (replace it if it is), the circuit breaker is not tripped (re-set it if it is) and/or the "reset" button has not popped out (press it in anyway!).
If all that has been done and the oven still does not heat, test the heating element(s) (LINK to instructions
If the heating element(s) are good, that leaves either the oven control or a circuit board, for which it might be wise to have a professional take a look.