It sounds as if the keyboard driver has changed.
MS Help says:
To switch languages or keyboards
Open Regional and Language Options in Control Panel.
On the Languages tab, under Text services and input languages, click Details.
Under Preferences, click Language Bar.
In the Language Bar Settings dialog box, check that the correct language and country is set for the keyboard.
To open Regional and Language Options, click Start, click Control Panel, and then double-click Regional and Language Options.
The letters on the icon in the task bar represent the active language. For example, EN stands for English.