2004 Mercedes C240 won't start

Hello guys and gals,

Ok, so here's my situation. Went down to New Orleans for
a few days and valet guys drained my battery down to
nothing twice and just jumped the car off before bringing
it to me. When I get back home, car won't start without a
jump. So, I went and bought a brand new battery. Started
and drove just fine for a couple of weeks.
Drove the car Saturday and then to work today, but as I'm
trying to leave work, I put the key in the ignition and turn it
and nothing. Lights come on, dashboard screen comes
on, a/c comes on, and ( and this is important ) my radio
comes on and is showing 12.6 volts on the battery.
So, just to be sure, I took my Halo Volt and tried to jump
it, but the Halo wouldn't give me a green light to jump like
it should. It just kept shutting off. So, instead, I got a guy
with a brand new S series to come give me a jump with
actual cables. Battery voltage showed 14.1 on the radio
when we hooked it up, but still absolute silence when I
turn the key.

Everything electrical seems to be working and turning on.
The battery seems to have power. I can move the gear
shift into neutral and park and turn steering wheel when I
turn the key into the on position and have my foot on the
brake. I'm just getting nothing at the engine when I turn
the key.

Any ideas?