HP Pavilion a6500f displays nothing

Hello, I'm working on a computer for a friend and I'm a bit stumped. The computer is an HP Pavillion a6500f running Windows Vista with a Foxcon motherboard and Phoenix BIOS. When the power button is pressed, all the fans go on, all the drives start, and the keyboard flashes, just like normal. The screen doesn't do anything, however. No beeps.



The problem started when my friend got some piece of hardware for an internet phone and attempted to connect it to his computer, connecting the hardware to the router first, then to the ethernet port. I don't know what the piece of hardware is, honestly. My friend is Korean, and he got it from Korea. All the details on the label are in Korean, and I haven't got a clue what it says.



After he plugged in the hardware for the first time, the computer froze. Over the next couple of days, it froze several more times and gave him some BSODs. After a few days, the screen just wouldn't display anything anymore. He brought it into Best Buy, and they told him it was dust on the motherboard that caused it to fail, saying he needed a new one. I think they were just trying to sell him a new computer, because it would've been an incredible coincidence that the motherboard failed because of dust when he plugged in the new hardware, and besides, it worked for a couple of days afterwords. I've reseated the memory and all of the cables as well as dusting it. Any suggestions would be appreciated. Thanks for the help.

To update, I've now swapped the memory dimms around and tried them one at a time in each of the two slots. I've tried replacing the old power supply with a working power supply and nothing changed. I've disconnected all the drives and hardware except for the monitor and still haven't seen the HP splash screen. I'm not sure what to check now. It seems strange to me that the problem escalated from occasional freezing (no mouse or keyboard response) to no monitor response in two days. I can't think of anything that could make it act like that anymore.

Were you able to get this fixed by any chance? I just ran into this problem with a friends a6500f. However it was not correlated to any install of new hardware/software. Just froze, rebooted and now NOTHING on the screen....the monitor actually goes to sleep while connected. Tried new video card, still nothing. Cant figure it out.....