What kind of computer should I buy?

I don't know very much about computers so please try to keep it simple. I like to use my computer to watch videos on youtube, play games on Pogo, and mess around on. I'll use it with some pretty basic music recording software so I MAY get some upgraded speakers and may get some upgrade on the sound card too, but I basically want an affordable desktop that will not be immediately obsolete. So if I were to rank criteria in importance it would be: 1) Affordability 2)Ease of use 3)Speed for video 4) Sound capability.