I have a problem here. When I want to type [shift + 2], it came out as " instead of @. When I want to type [shift + 3], it came out as ? instead of #. What is happening? Please help! Thanks a lot!

You have probably got the wrong language set for your keyboard/Windows install. I think you are looking for the US language option and you have the British option selected

All you need to do is go into Control Panel > Regional & Language Settings > Regional Options and go thru the options making sure that your preferred language is selected. "Apply" and ok to come out of it when you are happy with your settings.

I want to choose English (United Kingdom) instead of English (United States). How am I going to do that?

Just follow what Hengis said above and select English (United Kingdom) in the "drop-down" list on the Regional Options tab AND at the bottom of that tab where it says Location....change that to United Kingdom .

Ok, this solves the problem. Thanks a lot! =)