I changed something and now nothing is working, how can I fix it?

[Rob Swan]

Re-trace your steps, mull over what exactly you changed, and then try you best to undo what you did.

If it still does not work try a re-boot, ask google if necessary.

At the end of the day there is nothing that cannot be fixed (maybe apart from a hardware fault) by a full re-install, but then of course you can learn from your mistakes.

There is no shame in having to re-install, its happened to me a few times.