1991 Oldsmobile Cutlass wont start

I had problems starting my olds a couple months ago and ended up replacing spark plugs and battery, then reverse stopped working and all other gears work fine. I bought another car and let the ols sit for a week and told my sister she could have it as long as she fixed it. Long story made short, she drove it home and parked it no problems until she went to start it again. The dome light and all other electrical come on when turn key to run then when you try to start it, everything shuts off and quite high pitch sound occurs. I take key out the sound still continues not even the electric lock work! Could you give me some ideas on what to check or look at to fix my problems please? I am a woman but I know a little bit a cars, but not enough to figure this out