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[Lord Magnus]

Are you downloading stuff at the same time you're playing on Live ?
That would cause a bunch of lag.

Also, wireless routers usually stay a little behind wired connections, and you might have higher ping times than when you runned your connection straight to your xbox.

About being unable to connect... tell me what step of the troubleshooter it stops, and what error message do you get?
Also, while we're at it, after it's done with the troubleshooter, press your Y button and post your XYZ codes.

One thing I can suggest, and it's never a pointless thing to do, is a power cycle. That's the first thing xbox live customer service would have you doing. So do it just in case.
If you need instructions, follow this guide on how to Hard power cycle.

Good luck.