I hope someone can help - I have recently installed Magento 1.9 and have configured it sucessfully so that both the frontend and backend are visible (demo only).
However when the admin panel loads and the user details are inputted the log in page just reloads and won't let me get passed this point. The page loads with a new key at the end of the URL each time and if the inccorrect username or password are inputted this is detected and renders with the relevant error.
I have looked around and a lot of people have advised amending the varien.php file which I have tried but the problem still persists.
If anyone could offer any advice or help that would be great!
Might sound like a stupid question, but have you tried a different browser or tried flushing your current browser cookies?
I often have this issue and a simple browser switch or cookie clear does the trick.
Maybe you'll need to check 2 configurations:
1) Cookie configuration
Inside the backend you'll find that option into System -> Configuration -> Web -> Session Cookie Managment (I don't remember the key into database right now).
Sometimes the Cookie Domain and Cookie Path values can block the login if you've improted the database from another domain.
2) If you're using htt://localhost/ instead a qualified domain you won't be able to login.
I'm having the same problem, although none of these suggestions are applicable.
This is so frustrating, IE is still the single most used browser and to have these kinds of problems makes no sense.