An error message on a blue screen and uses the MS-DOS font. This happens when major or "fatal" errors occur. In some cases you can press any key "to continue," but sometimes pressing CTRL+ALT+DEL may be required, and in rare cases you will have to power off the computer due to the keyboard not responding or getting a "System halted._" message.
Windows ME sucks. I get blue screens of death 24/7.