Why can’t I download my game?

That's odd, is this the only game that you're having an issue with?

Okay, I tried unplugging the external and powercyclying the console. But the game still won’t download

Yes it’s only MW2 that won’t download

Let’s then perform an extended powercycle and reset your network hardware by following the steps below:

“1. Unplug the power cable from the back of the router, modem, or gateway for 5 minutes. If you have a router and a modem, unplug the power cable from both devices.

2. Press and hold the Xbox button on your console for 10 seconds or until it turns off then wait for 2 minutes before turning it on again.

3. After 5 minutes, plug the modem or gateway in first, and wait for all the lights to return to their normal state.

4. If you are using a router, plug in the router and wait for all the lights to return to their normal state.”

Now please try downloading your game again.