How to fix error can’t login to Magento admin panel

You have installed Magento. It works well for a time. Then one day you can not login to the Magento board. Do not show an error or any other messages.

There’s a number of different issues that cause the errorless admin login behavior you’re seeing, but they all go back to Magento not being able to set or read the session cookie. Magento uses sessions to pass error messages between pages, that’s why you don’t see an error message. What you need to do is find why that error and solve it. Below are some reasons and solutions.

• Local computer time vs. server time mismatch, causing instant cookie invalidation. Make sure your server time is correct.
• Incorrect permissions on var/session, preventing session files from being saved
• Incorrect configuration of database/redis/other session storage, preventing saving of session values
• A module is instantiating sessions to early, preventing the correct session names from being set
• You’re a developer using multiple URLs and have multiple cookie domains
• Another developer has somehow modified appcodecoreMageCoreModelSessionAbstractVarien.php, creating a hard to track down bug
• The cookie domain in System -> Configuration -> Web -> Session Cookie Management doesn’t match the actual site domain.
• You’re using the localhost as your server domain, and using a version of webkit that has trouble/bugs setting cookies for localhost in some situations.

The short-term fix is to just delete your cookie for the domain. That’s often enough to solve the problem.