I mean evrything, so that it looks like a default US installation:
Control Pane l/ Region and Language.
On the first tab, select "English United States", then click the Addition Settings button and ensure that everything on there matches US standards, then click OK.
On the Keyboards and languages tab, click Change Keyboards.
Ensure that both US and UK keyboards are installed, and that the default input language is "English United States"
Click OK, then OK
Restart the machine.
Repeat all the above, but ensuring that you set everything to the correct choices for UK.
Restart the machine.
To avoid accidentally switching to the US keyboard:
Go back in yet again
On keyboard and languages, click Change Keyboards
You should have already set the default to UK, so now highlight the US keyboard in the list and click "Remove"
Click OK, then OK