Gran Regal starting problems, oil pressure

I don't know the year off the top of my head, so I'm hoping for at least general info.

The car has been sitting for a few months, but I've been idling it once every few weeks.

Today it started up fine, but had a high idle. After a few minutes the idle went down a bit, but the service engine light came on. I turned the car off for a minute, then wanted to start it again to see if the idle would be better and if the check engine light would clear; but I couldn't start it.

It sounded like it was trying to start for a few seconds, but then there was a very distinct change in the sound of the starter. It went from the pulsing "eh eh eh eh" kinda sound (what you normally hear before a car starts) to just sounding like the starter motor was spinning free - i.e. no more pulsing.

After this started happening, I noticed the oil gauge is maxed at about 120 while the car is off, and putting the key to the on position causes it to go even higher. Not sure if that's related, and sadly I didn't notice exactly when the oil gauge did this.

Thanks for any help you may be able to give.

Sorry for the double post, but long story short I fixed it.

I was literally like panicking because the car isn't mine and I thought I may've blown the engine by not seeing the oil gauge reading.

Turns out... the battery was too low. It was at like 10.5 volts. So I hooked it up to a jump starter box. With the jumper connected I turned the key and IMMEDIATELY the engine turned over and was running great. Also the oil pressure dropped right back down to the normal mark.