How can you download halo for free on your computer

Basically, I don't think you can. There are videos on YouTube but I have the CD for Combat Evolved A.K.A Halo 1(if that's the one you're talking about) and it asks for a CD key and if you try following one of those YouTube videos it most likely won't work. I tried to do the same thing with Halo 2 and people were complaining about game related issues not working or about it asking for the CD key in the comments. If you're talking about 1(Combat Evolved) it most likely won't work because both games ask for a key. Sorry to hurt your feelings but it's true. If you're young, maybe you can ask Santa for it on your Christmas List. (Yes I believe in Santa even though I'm 13, haha). Or you can ask your parents to buy it for you, or if you have your own cash money or a bank account with a credit/debit card (must be at least 18 for a account) you can buy it yourself online or at a local store. Halo 1 and 2 can be played on the computer, I don't know about the others. So if you're talking about 1 or 2, you might have luck!

P.S.: Here's some news you might want to know. Halo 4 is coming out next year in 2012 between Christmas and Halloween.