hi-lighted desktop icons

OS:Windows XP

click once, click all. both mouse and keyboard functions select multiple items on the desktop. If I click one app to open, all of the selected apps open. No matter what application I’m in, I can not select just one item. In email, I click one email and decide to go the next email, and both get selected. I have had this issue reoccur several times in the past with different users, and we have either restarted the machine, or replaced keyboards and mice. However, replacing the hardware never really trully works. any ideas?