You can sort out the keyboard settings from within your control panel. You've not stated which version of Windows you're using. In Millennium (which I'm using), 2000 and 98 you go to Start > Settings > Control Panel and then double-click on 'Keyboard'. I think that it's fairly similar in XP and (despite Microsoft's unerring ability to make simple jobs successively harder with each release of Windows) it's likely to be similar in Vista.
Once you've got into the Keyboard settings, you'll probably need to click 'Add' to bring up 'British' as a keyboard option and then check that it's set as the default option.
The reason you can't set the resolution to the required setting is because you've not installed the driver for the video card (or onboard video). The driver should be on a disc which came with your PC. If not, you'll have to download it from the internet.
Chris
PS: If you experience a similar 'messing up' of your PC in future, please remember that it's always best to try installing Windows 'on top of itself' (i.e. without reformatting) before taking the drastic step of formatting the drive. In the vast majority of cases this will fix the problem without any loss of data (or drivers).