Sounds like your keyboard has been changed from what I'm assuming is a English (UK) layout to an English (US) layout.
The same thing happened to me, and it wouldn't change back, even under "Regional and Language" settings in the control panel.
No idea why it's changed, but to change it back, right click on the taskbar, go to Toolbars and enable language bar.
It should then be a case of clicking on the icon that should appear, and making sure that your keyboard is set to English(UK) and that no other languages are selected.