Movie that scared me the most as a kid

I saw that movie at a really young age (under 12 years old), and it is the movie that scared me the most in my whole life.

My grandfather had a whole stash of B-movies, and when we visited him, I would randomly choose a movie. I only saw this movie one time, and it was like 17 years ago.

I regretted watching this one... All I remember is that there was a girl who was in a big party and she decided to go alone in a room and watch a movie with demons on the television. Then demons went out of the television and she became a demon.

I remember that she lost all her toenails and teeths with a lot of blood, then she started to attack the party-goers. Eventually, they were all killed and transformed into demons.

Then there was a few survivors trapped in the high-rise building, but they could not get out. All the doors were closed and the glass windows could not be broken. Also there was blood and guts coming from some pipes in the ceiling.

I remember a bunch if black bodybuilders getting attacked and a pregnant woman stuck in an elevator or something.

Sadly, I was so scared that I didn't want to watch the rest of the film. For some reason, there wasn't many survivors left and I was convinced that everyone was going to die, so I stopped watching it.

I had horrible nightmares for months. Years later, I was able to rent Demons 1, but I never found Demons 2. I would like to see it again, and see how it ends.