How to Fix Magento’s Admin Login/Customer Login Failing (no error message)

[NoNick11]

I still have the problem anyone can help please.

[Finestshops]

check permissions and owner on var/session folder. I just saw in another post, that was causing an issue with logins - Magento could not write into that folder (files were 0 size). maybe try to delete that folder and create it again with permissions 777

[Pronto]

It usually happends when your staging and live environment use same cookies. Perhaps the easiest way to overcome this problem is to use browsers incognito / anonymous mode.