After replacing therminal paste on gpu and cpu i have problems with video. My laptop starts up lights come on but screen is black. WHen connected toTV thru HDMI it works fine,win starts as normal. Temp is fine, much lower than it was before. I don’t know what it could be, checked all screen cables.

If the screen lights up but shows no video, this is not inverter related failure. When inverter fails, the backlight goes off but it looks like in your case the backlight still working.

Did you try reseating LCD cable connector on the motherboard? Sounds like it’s either bad connection or possible video cable failure. This is just a guess. Cannot tell what is wrong without testing the laptop with spare parts.

My question is, where on the mother board is the “Nivia” chip located and is it reasonable to try to replace it?

The video chip soldered to the motherboard and you cannot replace it at home.
You can see it in the step 26. It’s on the right side from the CPU.
If you have nothing to lose you can try this method: http://www.laptoprepair101.com/laptop/2011/02/23/fix-laptop-motherboard-with-failed-nvidia-graphics-chip/

In addition, I wonder if there is another compatible chip that would work in its place and be more reliable. We really don’t need top of the line graphics performance. We don’t do any gaming and although the laptop supports TV (acts like a DVR) we haven’t used that either. We did pay a lot of bucks for this and part of my reason was to support an American company and trust in HP’s reputation (grrrrrr). Thanks.

No, it doesnt appear in “My Computer”. It suddenly completely disappear one day. When I start comp, DVD drive is running and green control light up but after Windows start, it is completely gone. When I tried boot from it, system leave a message “media test failure. check cable” or something like that. So that is why I think drive has a power but no data connection with Windows.

Sounds like your DVD drive failed.
The only way to be sure is testing the laptop with another working DVD drive.
I think you’ll have to replace the drive.

I have problem to recognize my DVD rom and I need to reseat data cable. Where will I find it or what have I open on my laptop to do that? I didnt notice on your pictures here.

There is no data cable between the DVD drive and motherboard. The DVD drive plugged in directly into the motherboard.
Try reconnecting the drive as it shown in the step 4. Just remove the drive and reinstall it back.
Test the laptop after that.
What do you mean the drive not recognized? Does it appear in “My Computer” at all?