CLK55 wont start wont turn over but all lights come on

Have you considered the possibility of it being a dead battery? Just sayin'

Possibility # 1 is dead battery.

Your system requires a near or fully charged battery to turn the starter as it takes a ton of amps. If you have a bad cell that will not hold a charge, you can't turn over the engine and the computer will not allow it. You have enough power to run the lights, locks windows and even the radio. If you can jump start it, and your amy shows a charge going into the battery, it just mayday be a bat battery. Have the battery tested before replacement. It could be a voltage regulator, or even corrosion on connections not allowing a charge to go into the battery. Unless you have the proper tools and skill set, it can be a bit tricky. Dealer or good honest repair shop. Even PepBoys can test a battery free of (charge) if you can take it to them. Be aware of batteries. Those made in China or even Mexico have a large failure rate. Pay to extra money. I just replaced my battery in my corvette and got a full replacement 5 year warranty. My mechanic told me to mark my calendar for 4 1/2 years after the insulation and bring in the battery for another new one. No questions asked on the warranty. Money well spent to eliminate headaches.