Ok this is what happened drove home from work (98' Sc300 with 140k) and turned off car, come back out in like 10mins car won't start. no click, engine doesn't try to turn over or anything. all i hear is the click from the rely. come back in maybe an hour car starts right up(i turn it off and on a couple times to see if it was a fluke and it starts everytime) so i drive it maybe 12 miles, turn car off won't start again. no click no starter sound. replace battery car starts fine and i driveit around maybe 40 miles or so turn it off and on a couple times and wait maybe 30mins-an hour between starts. leave it overnight car won't start so i was like ok maybe the alternator. so i pull it alternator is fine had it checked 3 times, battery is perfect too, or maybe starter? BUT when i put back the alternator allot of things aren't working now. headlights,dome lights,radio,factory alarm, electric door locks (windows work). i checked the fuses for these and they were fine, replaced them anyways and still nothing. i did replace the 120amp fuse for the alternator because that was blown. anyone know what i should check next?

 

i made a thread with the same problems. No Sounds or clicks when turning the key. fuses are all fine, month old alternator, starter was replace about 4-5 years ago.
if you find out anything let me know.

 

Turned out to be a short in the power cable to the fuse box. I dunno why I didn't check that

 

Have this same problem. Do you remember what power cable?

 

im having a similar problem man. all of my lights turn on and everything, exterior and interior, but my car wont turn over unless i boost it. let me know what you find and good luck.

 

Think this is happening to me too today changed starter and alternator and the battery is fine but when I go to start the car it sounds like it'll turn over but just won't. I smell gas getting to the injectors and all but still won't turn over

 

check for spark

 

Check your contacts on the battery itself and check the cables as well.