I am a novice any and all help will be greatly appreciated! I need to provide a list of valid usernames for cell #1, then have the user enter their password in cell #2. At this point I need to validate the entered password in cell #2 against the another sheet containing the valid usernames and passwords. If the password is correct they may continue on, if the password is invalid they must re-enter the password until it is valid.

I have been able to setup the List drop down box for the username, but I am able to continue if I enter nothing, I need to have a name entered from the list. Also I need to then have the user enter their password into cell #2 and then using the username and password from cell #1 and cell #2 verify the username and and password from another sheet using data from column a (username) and coulmn b (password). How can I accomplish this?
Thanks
JLW SR