Find the Keyboard layout icon to the right of your Taskbar.
Here it is on mine, indicated by the words ENG US - for English United States; press it.

This dialogue will pop up. This one shows a choice of ENG US and ENG ES (Spanish).

You may have a choice of one or two such layouts. The reason why when you press the # key you don't get a hashtag is that you are running a keyboard layout different to your physical keyboard layout. You need to find the one that matches your keyboard.
If you have two options, then try the other one.
If you only have one, then you need to press the Language Preferences button as shown above, and install the one that does match your keyboard.
If the # symbol on your keyboard is above the 3 then you need ENG US.
If it is on the lower of the two keys immediately to the left of the RETURN key, then you need a ENG UK layout.