don't waste your money on refurbished products. Just visit eBay, buy a used Dell desktop/laptop from a established seller.
Dell's desktops/laptops have everything (video, sound, network) on one board. So it's quite easy to identify the problem.
Many companies retire their PCs every two years. You can get very decent P4 under $300 from eBay.
Also www.craigslist.org is a good choice.