Undefined $pdo

i am getting a error in installation step 3
its giving error:
undefinded $pdo in install.php line 245

Hi techgamerz, welcome to the Gibbon community.

Sounds like a database connection error, or the PDO library may be missing. Which version of Gibbon, PHP and MySQL are you running? In Step 1 of the installer there is a check for extensions like PDO, did any of these checks indicate a red X rather than a green checkmark? Also, can you check your PHP error log to see if there’s any more specific errors in there?