01 PT Cruiser Won't Start

Three days ago we experienced extreme
temperatures, well into the negatives. We tried our
best to prepare for the weather; we put about
3/4ths a tank of gas in and put heet in the tank as
well. We tried to get the car to start the next
morning and no luck; same for day two. Once the
extreme temperatures broke, we replaced the
battery and while doing so the car alarm went off.
We got the alarm off and finished installing the
battery but still nothing. We thought perhaps it was
a frozen fuel line. Temperatures have warmed up
slightly and still no luck. The car almost kicks over
when we try to start it. There's no smell or clicking,
all of the lights go on and stay on along with the
radio. We're not exactly financially able to get it to a
shop right now. Did we do something wrong? Is
there something else that we can do to get it to
start? Or is a mechanic truly our best bet right
now?