C320 not starting

have you checked the alternator.? what relays are clicking thinking injector and fuel pump relays. also fuel pump fail will make engine not run or will run for a second or 2. on the injection line you will find a valve push this down if fuel squirts out then this is not the problem. but its more likely to be no fuel and you have flattered the battery. so it will need a good charge.

If the engine doesn't turn over it is not a fuel issues as fuel will keep it from starting. However the engine will still turn over what is more likely is a starting system concern since it just clicks it is probably the starter or starter circuit. again the fuel pump cut off only turns off power to pump which will cut fuel.. engine will still crank.

Check fuel pump relay and when it stops check for spark at the spark plug lead.

May need this:

Make sure the white wire to the pump has a good ground connection to the chassis. Then trace the power through the circuit opening relay. This is the most likely problem, as this is a dual relay. The relay coil gets battery positive from the starter relay, which you know is working or the starter would not turn. Check to make sure the white wire has a good ground connection. see diagram below.

At the moment, I'm only talking about starter relay. The starter relay has two sides, the load side and control side. The load side is that line with arrow, terminal 30 and 87, terminal 30 is hot all the time, plus, see that fuse on the load side. If you unplug the starter relay, key in the on position, on position is where dash lites come on, Then use jumper wire between terminals 30 and 87, at the least it should crank the starter motor and it might start. If you try that, make sure tranny is in park or neutral and parking brake is set.
If you get a reaction, the problem should be on control side of starter relay, right side in the picture. Terminal 85 and 86, the control side needs voltage and ground. You can see crank fuse, goes hot with key in the crank position, not only check fuse check for voltage on fuse circuit. As you can see, on the control side the neutral or clutch switch, depending on the tranny, is involved The ground for the control side is a chassis ground. As far as the fuel pump, other than the initial prime, fuel pump will not run w/o rpm signal, you have to crank it to get rpm signal.

Check the starter relay.

Check your battery connections, and your grounds for loose connections. This will cause the system to go haywire.

well the first part of your question i was all ready to tell you to put a new fuel pump in, now not so sure, there is a relay for fuel pump, can you hear pump cycle and relay click? relay under hood you will have to listen close they don't run long maybe a couple secounds, if you don't relay bad. if you do pump could be bad, do fuel pressure test pump could be weak. don't think sunroof and turn signals are related, but stranger things have happend.

It might not be the relay you are hearing, but the electronic fuel pump (located in the gas tank....yeh!!!) turning on and off. Have you had this checked out??