Hello Joe,
Firstly - welcome to
CompuForums. We provide our computer help for free, so we would highly appreciate it if you could help us. You can do this by answering other people's questions, or if you are not so technically-minded, post in our general lounge forum. Alternatively you can purchase a premium membership to help contribute to the rising running costs of this site. If you can't help us then we can't help you. This system allows us to continue to provide free computer support.
It sounds to me like the system physically has a problem with one of the components and will need service from [either from Dell or if it's out of warranty, your friendly local computer store].
The only other thing I suggest you try is reinstalling XP, or booting from a Linux live CD and testing typing text to rule out any software problems such as viruses.