Car shuts off when brake is pressed!

I have a '96 saturn sl1. I bought it
about 6 months ago from a friend of
a friend. When I bought it they said
brakes were replaced within the past
year amongst other things. It ran
totally fine. No problems for the past
6 months until a week or so ago. My
engine started to sound a bit loud so
I figured I was overdue for an oil
change since I drive on the highway
frequently and I was about 200 miles
overdue. I got it changed but it didn't
really sound much better. A week or
so later there was clanking coming
from under my car and then all my
lights inner and outer were flickering
just a little bit. You could only tell if
you stared at them. Then one day it
was very cold and I started to drive
it. I get to the stop sign press the
brake and everything flickered on
and off but the engine caught itself I
guess and kept going. That night I
am parked and my car had been
running for probably 3-5 mins while I
got the snow off and then I pressed
the brake while in park to see if
anything happened and the engine
and radio shut off BUT all the
symbols on my dash were lit up like I
hadn't turned my key the whole way.
I turned my key and started up the
engine and then I drove home fine
never did it again. I didn't end up
driving it for 2 days and it wouldn't
start. I got a jump let it run for 15
mins tried the brake and it shut my
entire car off engine and all and
didn't make a sound when I tried
turning the key! What could be
wrong?!?! Thank you in advance!