What you need to check in order to repair the error, is as follow :
- Go to your prestashop installation folder
- Go to /controllers/admin
- Find the following file AdminDasboard.php
- If you font find it, then you should upload the file from your prestashop folder at your computer.
The error message controller not found happen because the AdminDasboard.php is not exist. So, when you upload AdminDasboard.php to /controllers/admin and refresh your prestashop dashboard you will not see this problem again.