Issues with Dell Dimension 2400 Desktop.

Hello,
So, I've had this old desktop computer for years now, until it started giving me issues and lacked performance. I purchased a laptop a little over three years ago, and since then the thing has barely been touched.

Now, however, I want to get rid of it, since all it really does is take up space. Before I do so, I'd like to transfer any documents and pictures that might be on it onto my USB so I can keep them. The issue is that the thing doesn't want to work.

When I start it up, it'll load through Windows startup (it's equipped with XP), and bring me to what should be the desktop screen. But all it loads is the background image -- the desktop icons and start bar at the bottom and anything else that normal would appear will not load. What does happen is that it immediately presents me with a pop-up stating that "Userinit Logon Application has encountered a problem and needs to close. We are sorry for the inconvenience."

While the keyboard seems to respond (I can press enter while this pop-up is present and, as the computer is programmed to, it selects for me the "Don't send" option), beyond that it doesn't have any effect on the computer when I try to press keys.

Does anybody know how I might be able to make the desktop work long enough to retrieve my files and copy them onto my USB drive?