I have a 1995 BMW 740il after i got it when i changed the oil it kept giving me a message that says "stop! engine oil pressure" so i was wondering what that is exactly and about how much it costs to get it fixed?

Thanks

The oil level is full correct? Check to see maybe you knocked the wire off the sending unit when changing the oil.

actually that problem started ever since I change my oil when i asked people said the car's problems appear after changing the oil so if that really was the problem how do i fix cause i can't change my oil i had to go somewhere to do it what i am saying is do i have to go the dealer or can they just fix at the place where i got my oil changed?

The best is often to go to an official dealer of the make, even if it's a little bit more expensive, it's more secure. Personaly, to make the maintenance of my car (320d Touring now), I prefer to go to a bmw dealer. It's maybe 20% more expensive than in a private garage, but it is more sure. For the other makes, it's always arround 20% (I had Alfa, Bmw and Peugeot mainly, the difference is arround this figure). Then, when you've a new car, under warranty, you must make the maintenance in a dealer of the make or of the group. Otherwise, the warranty is not any more available.