Light Meter won't show up?

I'm taking a photography class, and It's our first digital assignment. At school, i could operate the camera perfectly fine, but now at home everything is going wrong.
I'm a complete beginner at this, so I really need some assistance here please.

In my hands i've got a Nikon D-80
I'm shooting in my bedroom, the light is attached to my ceiling fan. (Bright, but not very good lighing.)
ISO is 400.
White balance Incandescent.
The light meter won't show up and the shutter is extremely slow. The camera will not allow me to change the f-stop.

The shots are due in the morning so it would be great if someone can please help me.

Added (1). The mode I'm in is Manual.

What mode are you in?

The camera allowing you to change the f-stop but setting the shutter speed by itself would indicate that you're not in manual mode, but aperture priority mode (A mode).In that case it wouldn't show a light meter because the camera sets the shutter speed to an exposure that would read ±0 o the light meter.
Hence in aperture priority or shutter priority the light meter isn't actually shown unless you set an exposure compensation using the ± button on the top of the camera.

"The mode I'm in is Manual."
NO it's not or else the light meter would appear.

If the shutter is extremely slow and you are in manual mode as you calim to be, it's because you SET IT at a slow speed. Manual mode does NOTHING on it. Own… You have to set the shutter speed, the ISO and aperture. If the shutter speed is slow and YOU DIDN'T SET IT then you are NOT IN MANUAL MODE.