YouTube App was shut down in April 2015 by Google. To enjoy YouTube, open a browser on your device and visit www.youtube.com.
Alternatively, you may reset the device to factory default status by installing the firmware via a SD card. The firmware file and relevant instructions are available in the Philips website.
(Note: Any installed Apps or file saved in the device would be lost after reset to default status.)
For more information you may visit https://support.google.com/youtube/answer/6098135 .