If your keyboard is erasing letters as you type, you have probably turned on overtype mode. When you type in this mode, you erase any existing letters to the right of the place where you are typing. This mode is useful if you are trying to type and delete old text simultaneously, but if you are not trying to accomplish this, you should turn off overtype mode.
Microsoft Word 2003
In Microsoft Word 2003, you can determine if overtype mode is turned on by looking at the status bar to see if "OVR" appears. If it does, you can turn it off by double-clicking on the letters. You can also use the Insert key as a shortcut to turn overtype mode on and off.
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Microsoft Word 2007
In Microsoft Word 2007, you check to see if overtype is turned on by clicking the Office Button in the top left corner of the screen, selecting "Editing options" under the "Advanced" tab, and looking at the "overtype mode" check box. If a check mark appears in the box, overtype mode is on. If you want to turn it off, uncheck the box.
Open Office Writer
To see if insert mode has been enabled in OpenOffice Writer look at the gray box at the bottom of your screen reading "INSRT-OVER." Click the box to switch back and forth between insert mode, in which you insert text without erasing it, and overtype mode. Like in Microsoft Word, you can also use the Insert key as a shortcut to perform the same function. If you want to remove this box from the bottom of your screen, click "Tools," select "Keyboard" under the "Customize" tab and remove the "Insert mode" command.
You can see if you have enabled overtype in Word Perfect by checking the overtype box at the bottom of the screen. Either double-click the box or press "Insert" to enable or disable this mode.