After replacing the battery, car cranks but will not fire, 01 Volvo s60

Hello, It may be an immobilizer issue, and, if so, you should have a security light blinking or illuminated. Try using the spare key if you have one, and, if not, check your fuses to make sure that power surging did not destroy one when the battery was reconnected. If the vehicle lost the memory for your key while the battery was out, you will just need to perform a relearn for the key, but may have to replace it with a new key.