I'd agree with most of the comments so far. You may want to add a simple, recognisable company logo rather than the PC on the desk. This would also be a help when printing out business cards, as it's always best to have a consistent 'look and feel' on all your promotional material. The same applies with whatever font and color scheme you decide to use.
As mentioned, i'd make the font larger and get rid of the background image. Regardless of how it looks, it will become very printer intensive if/when you decide to print more posters. Also, it won't be as clearly defined when actually printed.
Is that phone number a dedicated business number, or a home number? I'd make sure that it's always answered with "King Computers", rather than "Hello". Make sure you (or someone else who can take calls for you) is always contactable, many new clients won't bother calling back if they can't get hold of you quickly.