First, (and probably the best and easiest option), if the system was running fine a few days ago, then use the System Restore to go back to a time when things were good. That should do it. Click on the link below for instructions:
http://support.microsoft.com/default.aspx?kbid=306084
If that doesn't take care of the issue, then you'll need to reinstall the "Accessories" part of the Windows Installation. You'll probably need the Windows XP CD, although many times it's not necessary. Log in as "administrator", then click on Start-Control Panel, the double click on the "Add/Remove Programs" icon. When that opens, click on the "Add/Remove Windows Components" button on the left side of the window. When that loads, highlight the "Accessories and Utilities" line, then click on the "Details" button. When that loads, UNCHECK the box next to the "Accessories" line, then click on OK and follow the prompts to uninstall the Accessories programs. Restart the computer, then follow the same procedure, except place a CHECK mark in the "Accessories" option and reinstall the programs.
Hope this helps.
Grif