What we have here is a "failure to communicate" (Paul Newman, Cool Hand Luke)
I am having great difficulty understanding what you are telling me.
First, to do a voltage check, plug the meter leads in the common and the V holes. Next turn the meter dial to the squiggly line in "V" or voltage section. The squiggly line is for AC, the solid line with the dotted line underneath is for DC. Check your meter and its set up by inserting the leads into outlet you know works. You should get a reading of approximately 120 volts.
To actually do the voltage check, you touch one meter lead to the white wire and one to the black or the red wire.
Please learn to use the jargon.
A box is the plastic or metal box where the wiring connections are made. In this case we have a switch or outlet box and a ceiling box. The ceiling box is the actual box where the connections are made and the fixture or light is attached. The fixture or light is the actual light it self.
A wire is a single wire. A cable is two or more wires in an outer covering. You can have 2-wire cable with a black and white wire, and 3-wire cable with black, white and red wires. We don't count the ground wire because the actual correct terminology is 2 or 3 "conductors" and the ground is not a conductor. It is difficult to follow your post when you use the term wire to mean a single wire at one time and to mean a cable at another.
Please edit your post. Enter your post, wait 5 minutes and then read what you actually key in. You have to wait a little while to make yourself actually read what is there, and not what you think is there. In your last post you used the term "dead" several times. I can't tell whether these were just typos and you meant to type "leads" or you mean a dead or unused wire or cable.
Did you install the light fixture that you currently have and if so did it work before you started with the switch replacement?
Where the light fixture is is where the power is coming in on a line with red reading 24 volts black reading 120 and white with no read.
There is also another line with red black white dead that runs into the switch box.
I am reading that to mean that there is a 2-wire cable and a 3-wire cable in the ceiling box.
Along with this is the black and white wires from the light fixture.
I read that to mean the black and white wire from the actual light fixture.
To summarize my understanding, in the ceiling box you have a 2-wire cable, a 3-wire cable and the black and white wires for the light fixture. If that is correct you should have the white wires from each cable and the white from the light fixture all connected together. The black of the 2-wire cable may be connected to the black of the 3-wire cable or it may be connected to the red of the 3-wire cable. The black of the light fixture will be connected other wire (red or black) of the 3-wire .
All of these wires mentioned above are in the hole where the medicine cabinet goes.
I am reading that to mean that theses cable simply pass through the opening in the wall made for flush mounted medicine cabinet.
In the switch like I said before is the dead black red and white in one line also are a black and white in a line the white dead black reading 4 volts... Weird.
To me that means that in the switch box you have a 2-wire cable and a 3-wire cable.
Another weird note there is one room in my house along with one hallway fixture that don't have power since I unhooked the original switch.
Not strange at all, it is indeed what I would expect. Some where in the process of replacing the switch or replacing the light fixture you have disconnected the wiring to those fixtures. May seem weird to you but perfectly logical to me.
So do the voltage checks again. Confirm the wiring in the ceiling box .
Footnote:
I spent 45 minutes keying all this in. I then spent another 15 minutes editing for typos and also editing to try to insure that I said what I thought I said. It is simply what you have to do with written communications. Even so, I am probably not completely clear in what I am trying convey.