No oil pressure but no knocking or overheating. Not starting

Usually when I have a problem I have an idea on what it is but this time I'm clueless. The first thing that happened was I shut the car off and it didn't start after that. It seemed like the terminal connection was loose because when I turned the key all electric went off and then when I let go of the key everything came back on. No clicking just lost all lights, and electrical power. Checked the battery connection and it was tight. The car has a brand new battery, Terminal connecters and alternator. After getting a jump the car started and started without trouble the rest of the night

The next day I started the car and a good amount of white smoke came out the exhaust but eventually went away. Had the car running for 20-30 minutes and noticed the car wasn't getting warm as quick as normal. After that while idling the car seemed to run rough and when I looked at the gauges the oil pressure guage read zero. Right away I turned the car off and checked the oil. I was a quart low and I filled it to full. Scared to run it if it had a bad oil pump I went and bought a new oil pressure sending unit and replaced it.

I went to go start the car and battery was somehow dead. So I had a booster pack and tried jumping the car. It wouldn't start with that or with a friends car and jumping cables. Even with the jump it seemed like it didn't have enough juice and made a whining noise. I took the battery to Autozone to have it charged. After it was charged it put it back in the car and tried to jump it.

It now has enough power to turn over but no matter what it will no catch and start. Everytime I try it just keeps turning but no matter what does not catch. At this point I don't even know what to try next. Any help or advice would really help me out. Don't have slot of money to take it to a mechanic. I have a friend that will do work bit I need to first tell him what to fix. Thanks in advance for any help