Ubuntu – Is Ubuntu Desktop free for a business solution

Yes, you can charge for it. The only restriction is that you must provide your customers with the source code to the software. Provided that you don't modify it, that is already handled by Canonical and the Ubuntu archive mirrors.

See also:

http://www.ubuntu.com/project/about-ubuntu/our-philosophy

No, this does not refer to how you use Ubuntu, but rather how you distribute it. You can use your machine in any way you like basically as long as you don't start selling Ubuntu because it's not your IP (Intellectual Property).

That's all that this refers to, it's nothing for you to worry about, you can use your machine for commercial gain as long as you don't try to sell Ubuntu.

(To be precise the non-commercial clause you cite refers to the trademarks of and surrounding Ubuntu and its manufacturer Canonical. Since Ubuntu is distributed only with free open-source software, you're welcome to take Ubuntu, remove all references to its name and redistribute its software however you like – in accordance with their licenses – including for monetary gain).