The X sustain board is used in the discharge phase of the Plasma panel.  Circuitry can fail to function without a fuse having to blow.  As stated, at the very least you have a bad X sustain board, it's quite possible you have another problem as well, quite possibly including the panel itself. 

 Philips doesn't supply individual parts for the boards nor is the service info useful for troubleshooting. In fact, IIRC, there isn't a schematic for either of the sustain board circuits. Plasma TV's are nothing for anyone to be messing with as far as troubleshooting to component level. They were designed from the git go as board level replacement.

BTW, most of the manufacturers are extremely secretive of their firmware and chip architecture in both Plasma's and LCD sets.  You'll be unable to hook any laptop up to that set because philips would never allow the software to access their sets into anyones hands other than their own.

  One particular Plasma TV manufacturer has their set booby trapped.  If you attempt to fire the set up with the back off and not have the hidden safety switch set you'll completely zero out the EEPROM effectively killing the set.  Completely.  Dead, nothing until you take it to that manufacturers authorized service center to repair your mistake which will wind up costing you a very expensive main board.  

I have the Philips 42PF5321D-37, I recently upgraded the firmware because I was having a problem with the red light blinking 4 times.  That problem seems to be fixed but now when I turn the tv on the green light comes on for about 15-20 seconds but then goes out, there is no sound or picture.  I have unplugged it several times, let it sit overnight and still it wont work.  When I initially plug in the power cord it clicks, turns green and goes off, that is normal but then when I hit the power button (on the remote and on the side) it wont click like it normally does when it's powering on just the green light pops on without the click.  I hipe I explained it clearly and someone can offer some suggestions.

Thanks

Same thing happening to me after I upgraded the firmware as well with the green light on then it goes off.

It was done as per instructions on the Philips site, Yes it was unzipped first and it ran automatically. Where is this small board located.

Well no it is turning on but I dont know for how long its going to work, the menu and screen are sometimes flashing when it first start's, Video card or Power board?

Make sure you unzip the file and put only it on a USB drive should work