Do you have experience building PCs?
I would assume you know just enough to troubleshoot some issues, but if you are able to, price out a new PC for him. Find his price range, and go to sites like newegg and price one out piece by piece. It's cheaper, and you get way more for the money doing that.
If you don't do that, or are not comfortable doing that, make sure you do not send him out to Walmart for a computer. Please? Find a reputable PC shop in the area, or a friend that can do this sort of stuff ... or hell, email me and I will price something out, just don't buy a PC from Walmart.