You can directly check the user in database if anything wrong. Or you can also change the password for that user as well from database directly as Magento 1 uses MD5 encryption for admin password.
You can create a custom script and place that to your magento root and run through browser. That will create new admin user then you can login to your admin through that user and then reset the password for previous user accordingly.
Script for create admin user programmatically:
$user = Mage::getModel('admin/user')
'username' => 'your_username',
'firstname' => 'YOUR FIRST NAME',
'lastname' => 'YOUR LAST NAME',
'email' => 'email@example.com',
'is_active' => 1
//Assign Role Id
echo "User created successfully";