Will not turn over

No such thing as a sincere relay, there is a crank sensor and camshaft sensor as well as an ASD relay that and any of those bad can case the car to not start. Try wiggling cranks sensor wire and look for a bad connection see if starts then. If not scan for codes and check fuel pressure with a gauge auto parts rent it. As low fuel pressure can be a cause of a no start as well.

Wont turn over as in you turn the key and the engine does nothing? O do you mean you turn the key and the engine turns but doesn't start? Two different issues.

If it is the first item, it could be a bad battery, bad connections, bad starter, bad starter solenoid.

If the latter it could be many more things. Low or no fuel pressure, no spark being the most common. The cam or crank sensors may not be the problem. It could be a single fuse to the engine computer or a broken wire. Or even a security problem that activated the immobilizer system and is preventing the engine from running.

As for a sincere relay, never heard of that. Maybe the Auto Shutdown Relay? That is the relay that controls the power to the engine control systems on your vehicle. It is in the under hood power center. Or the Emergency Shutdown Relay? Located in the same box under the hood. It shuts down the power if the alarm/security system is the problem.