Recommend me a desktop

With me going away to school this fall, I won't be able to help my mom as much as I normally do with the computer. So I need to find her something new. Her current desktop is starting to show it's age, and is unfortunately too old to just replace individual parts.This has been a desktop that has gotten me through middle school and my junior year of high school, and then has proceeded to help my mom with bookkeeping and any other simple tasks.

Ideally, what I'm looking for is something that can do the basics: run Outlook and occasionally Word, watch Youtube, play some solitaire, use her bookkeeping software, and run Skype without too much issue. Camera wise, I don't have an issue picking up a USB webcam to fulfill at least that.

My mom isn't tech savvy, so it needs to be something she could get the hang of without me being in the other room to play IT for. She really has some hate for computers, but understands that she needs to use them to keep her business financials in order and to stay in touch with family.

The ideal price range would be under $400, no need for a monitor unless it's a major free upgrade - and even then I might use that for myself if she saw no need for it. If it's possible to go lower on the price without damaging the quality, even better.

Thanks for your suggestions, I really appreciate it!