I use an Administrator account and a user account and keep switching between the two often. Is there any keyboard / mouse shortcut to switch quickly between the two users? Much better if it doesn't prompt for password everytime!
You can switch user (ie. Lock) by using the shortcut Windows+L.
If it does not prompt you for the password, it means there is no password (ie. it is disabled). Based on How to remove login password from windows 8 logon and login automatically without entering it, you should:
Un-check the requirement to enter username and password.
Remove any passwords set.
Alternatively, you can run as another user:
runas /savecred /user:domain\user "notepad"
If you do not know what domain and user is correct, you can ask
> whoami domain\user