History:
Bought the house a few month ago, there was a TWO prong outlet over the mantle that I want to plug my TV into but it didn't work. I didn't put a tester on it until after I tried replaced it but I used a working lamp and it didn't work.

Now:
I bought a surge supression outlet ($20 a homedepot). I have a metal box and the ground is coming from to the wall somplace and screw down into the box. I bought a ground wire with a nut and connector on it, unscrewed the box ground, used a wire nut and put the new ground wire and new ground together, then put the connector under the nut on the box, and another connector under the nut on the box and went to my outlet.

I tested it and its saying I have an open ground. What things should I look it, I have a multimeter, what should I do with it to further test?

I have an outlet in a different room on the SAME wall that I knew didn't have one plug working so I tested it, open ground as well. The bottom plug works, the top doesn't on that outlet. It's seems possible that they could have tried to come off that outlet, if they spliced from that top plug on this outlet, and the outlet is bad, could it be not working because its just a bad outlet?

I would test other outlets to see if they have a ground. You could have no outlets grounded, a disconnect somewhere or your building ground is bad.

The other outlet may be wired up to a wall switch. If a switch is nearby plug a lamp into the non-working side and test it

If only on a couple of recepticles, I would determine what circuit it is on, turn the breaker off, see what recepticles are on that circuit, and see if they have a ground, maybe a ground not made up in a box.
The receptacle should have power even without a ground. You need to have 120 volts between the Ground and the small prong(hot), and you should have 120 volts between the ground and the small prong. Ground and neutral are at the same potential, neutral carries current, ground does not, unless a fault occurs. If half a receptacle works, the other half may have had the tab on the side of the receptacle removed to allow switching. Try different switchs, may also control receptacle over the fireplace?