I am using WordPress v3.3 with "PDO (SQLite) For WordPress" plugin v2.7.0.
After I installed and activated "W3 Total Cache", I got white blank screen. It turned out that, "W3 Total Cache" wiped my db.php file and replaced it with its own.
Everything is running fine after I manually removed everything related to "W3 Total Cache" including cache switch line on wp-config.php, then restored my db.php from backup folder.