Car wont start

I replaced the harmonic balancer and before I replaced it the car started fine, now it has no spark going to the plugs I checked all the fuses they are all ok, what could cause this?

I have a Buick Park Avenue Ultra. And I have an no start problem I just replace the starter and still no start. Tried to jump off no start it will not rotate at all I replaced the battery and the car will not turn over.

Thank you

I have a buick park avenue ultra. And I have an no start problem I just replace the starter and still no start. Tried to jump off no start it will not rotate at all I replaced the battery and the car will not turn over.

Thank you

Engine starts and runs fine. Sometimes after turning off the engine it will not restart for anywhere from 10 minutes to an hour. It cranks but doesn't start. Once it starts it runs fine. It has been happening more frequently. It has been in the shop and they said everything checks out alright. They kept it and drove it for several days and it started everytime. Could the crankshaft position sensor test good but still be causing the problem?

We found the front seal leaking and oil was found on the crank sensor. Could this have been the problem? Time will tell.