Welcome to the wide range of users who have had dead Touchscreens.
You can try to do the "Needle method" described in this thread:
[Link: remotecentral.com]
You'll most likely find the method described on one of the last pages.

And, try to search the forums or read through the above thread, there is a number of solutions which may or may not work.

If nothing helps, you'll need to be a replacement touchscreen. Search the forums for instructions.

If it's possible try to get an replacement from your seller or Philips (better: seller)