Do the electronics in the vehicle work? I mean do the interior lights come on, and if you turn the key will the radio turn on and what not?
If not, then it wont be your starter... A single click leads me to believe that your battery is very low on voltage and only has enough juice to turn the starter over a single time and then its cashed.
Its possible something is draining your battery. I had a situation a while back where a couple strand of my 12v lead from the battery were touching the REM terminal on my amp, and it drained my battery over night...