Computer Keeps Shutting Down without Going to Sleep

I didn't read it all, as it is a lot to read. Maybe, it's my ADHD or ADD kicking in. I just read the first page. I haven't changed any settings though.

What do you mean?

Do I select power, and then sleep?

The tower doesn't look like its sleeping, but the keyboard and mouse sort of does. But, when I press enter to wake it back up, it won't wake up.

The monitor is sleeping.

It's lit up, but it won't wake the computer. Also, when I press enter, the Number Lock key flashes once, but then goes back off and the keyboard refuses to wake the computer.

It shut itself down.