When you say you can't login, is it that you get the option to log in but its not accepting it, or you don't even get an option to login.
If its not accepting what you are putting go to google on your PC and login to that then make sure you use the exact same details to
log in to to you phone.
You could reset your google accounts on your phone
go to setting>applications>mangage application find your Gmail and clear data also Gmail Storage clear data, also check google apps and / or google apps storage if listed and clear the data there.
Now try accessing the Market and if its cleared the data you should get asked to setup your account
