2002 Chevrolet Suburban Won't Start what could be wrong

My 02 suburban is not starting. When i get in and turn they
key it does nothing. My radio lights and all that work so I
don't think it is the battery. About 3 weeks ago I had to have
my fuel pump replaced and my instrument cluster fixed. I
also had to have a new ignition key made due to losing my
original. A week after having it fixed code p0440 came on
and shop said it was gas cap and he turned the light off. It
came back on 2 days later. Also the past 2 or 3 days i
notice it doesn't want to go into park when I try. I have to let
it roll a tad bit for it to go in park an unlock doors an release
my key. Now it wont start at all. Can anyone point me in the
correct direction as to what could be my problem. Also
might I add I am a woman so you might have to explain a
tad bit better beings I don't really work on cars unless it is
something very simple.  Thanks Fe