In Magento 1x
try this query and check your url is correct or not.
SELECT * FROM core_config_data WHERE path LIKE "%admin/url/%";
and remove all cache from cache folder.
check these links too
"Error 404 Not Found" in Magento Admin Login Page
https://magento.stackexchange.com/questions/73228/where-is-admin-url-custom-path-in-magento-site-database-file
To change the Magento Admin URL / Path
open the local.xml configuration file ,is usually located in the
app/etc/
directory under your Magento installation.Then locate the following code segment:
<frontName><![CDATA[admin]]></frontName>
replace admin with your new admin path.
Then Use an FTP client to delete the content of the var/cache/ directory.
Magento 2
Change Admin Path
It is not recommended to change it directly from app/etc/env.php, always prefer the CLI:
php bin/magento setup:config:set --backend-frontname="admin_path"
Do not add the first / in the admin_path as it will result in an invalid parameter exception.
Change Admin URL
This can be done via the admin under Store > Advanced Tab > Admin Base URL section