How long have you had the set for and when did this problem occur?
Do the standard Component and AV jacks on the TV work?
If you press the MENU button on the TV remote (not the cable box remote), does the MENU come up on screen?
This is a failure in the HDMI circuit on the mainboard of the TV. This is the only type of cable that provides 5 volts of bus power to transfer the signal. It is very susceptible to surges, shorts or arcing at the terminal end of the connection. The HDMI inputs, or the entire mainboard (the board that routes all of the AV signals in the set), would need to be replaced. The average cost for this type of labor to replace HDMI Inputs is around $200 parts and labor. To replace the entire mainboard would run closer to $350 parts and labor. Unfortunately, there is no reset or series of buttons you can press to fix the problem. The TV will require component replacement in order for the HDMI Inputs to function properly again.
If you need further assistance, let me know.
The HDMI Inputs are not available separately, except at an Authorized Service Center direct from Philips. The mainboard itself can be found at the link below, and is roughly $100-$125 depending on the board. There are several different Mainboards used in your model number, you would need to open the set and get the part number off the board, and match it up with the Mainboards listed at the link below:
There really is no fool proofing these jacks. The best prevention you can take though, is use a high quality surge protector, line conditioner on ALL components connected to the TV and the TV itself. Never plug or unplug the HDMI cables when the units are in the on position. Beyond this, there is nothing more as a consumer that you can do.