what would you suggest is a good computer and why

Never buy a pre built computer would be my advice. If you buy a pre built pc you are overpaying for a under performing pc and if you spent that same amount on building it yourself you would get a much better machine. Even if you dont have the know how to go about buying and building your own pc there is a excellent website that allows you to pick from a list of components that match your price range and you dont have to worry about whether they will all work with each other because you will only be able to pick parts that are compatible with each other. The website i am talking about is Computerplanet. This very pc was bought of Computerplanet and i got MUCH better hardware by buying it from there than from buying it from a place like dell.

In fact I think if it's just for web surfing or daily file work, a really ordinary computer now will be enough for decades. But if you use it to play PC games, it should always be up to date I'm afraid :)