Is your keyboard language set correctly to US English (assuming you are working in English) if it has been reset bto another language the output will not be the same as the keystrokes.

keyboard set to EN English Ireland, as it ought to be. abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ ABCDEFGHIJKLMNOPQRSTUVWXYZ ABCDEFGHIJKLMNOPQRSTUVWXYZ now its working fine and I haven't done any changes. (That I can think of) Thanks anyway!

Windows remembers the keyboard layout setting per application and you may have changed the keyboard layout by accident via a keyboard shortcut.
See:

• http://windows.microsoft.com/en-US/windows-vista/The-Language-bar-overview - The Language bar (overview)

The default keys to rotate the layout is a combination (Ctrl+Shift or Alt+Shift) that can easily be used in Firefox to activate a menu item.
To avoid an unintentional switch, assign a specific key sequence (Alt/Ctrl+Shift+number) to select keyboard layouts and remove the key combination to rotate layouts (Alt+Shift or Ctrl+Shift)

• Control Panel > Regional and Language Options > Keyboards and Languages > Change keyboards > Advanced key settings > Change key sequence

http://support.microsoft.com/kb/258824 - How to change your keyboard layout