#1 Make sure the 6-pin & 8-pin power cables going to the gpu aren't pulling from the same 12v rail. Overloading a 12v rail will cause the computer to shutdown and restart by itself.
#2 Check for overheating on cpu/gpu while under load.
#3 Your psu may be faulty. Try a different psu.
#4 Card may be faulty. Test card in another system.

I'll upload 3 pics... One showing the power supply at the top with a handle to pull it out... One showing it removed and you'll see it just plugs in and the wiring is behind the mother board and I don't think it can be accessed.  3rd pic shows the cabling.  When I first got the graphics card I didn't look inside for the power cables as I have read there should be 2 6pin and I went and got adapters and it turned out to be 2 4pin with 2 I guess SATA connectors too... Microcenter gave me the adapter that you see.  On one end of the adapter there are 2 molex with one having 4pin and the other 2pin and on the other end it gets connected to the 6 and 8pin on the card.  I didn't trust this and I think you are right there is a power issue.  Since I can't connect cables to the power supply as its modular and just pops in without cabling how can I work around this issue.  Separate power to just the graphics card?  If yes, is there a write up on how it's done and what power supply would you recommend?
Greatly appreciate your knowledge and help
I don't see where I can upload the photos... guess I must edit original post and I don't see the original pic

I got around 66 seconds in Blender Benchmark but card is overclocked and real result is probably 2-3-4 seconds slower.
Yes GTX780Ti is good there.
 
Maybe other people use TITAN in HP Z800 or graphics with similar power consumption but what if over time PSU become weaker.
Shut down under full load and that easy restart and boot into Windows alone after 2 seconds is typical PSU problem.
If no normal Power connector to for 8+8 pin or 8+6 pin for at least 2 graphic cards than better looking for other PSU.
 
From other side on ebay anyone could sell anything, sick people don't think how others feel if they bought broken hardware as working and can't afford new.
 
You see, he replace PSU with some Super Flower 1000W PSU and could say two TITANs work in my HP Z800
 

 
 

Photos:   htt p://imgur.com/a/9lKjs     htt p://imgur.com/ZmYzXXs
I know it's hard to see from photos but the power cables come from behind the mother board and aren't directly connected to the power supply...
Vlada011, yea I figured the 780 ti would do well with Blender and that's what I was hoping for... Funny thing Nvidia said the GTX cards won't work in SLI with Z800s... only with Quadro cards...
Sajin, thanks for the help...  is there a simple way to power the card with another supply... I've looked online but only see old info from like 2006... Seams like there would be... like one of the 4pin power connectors connected to the power on switch of an external power supply so it turns on and off as the computer powers up. 

 
What are those two 6-pins for?

Sajin... looks perfect... exactly how I thought it should work... now i need to find one cause it's out of stock... 
Thanks so much!  I'll pick one up somewhere and get back to this thread asap...
Again... thanks!

Looks like it may be hard to find someone that sells them and they are in stock...

Bimmerfx
Sajin,,, l will shut down and take a look... aren't they connected to something?
 

I think they're just sitting there waiting to be used.

No problem. Report back when you can. 

Sajin, I'm up and running!... Greatly appreciate the help. 
I ran the 1M Plasma Particle Benchmark from EVGA,,, I'm not sure of how good the score is.
Score 16721 points ( 272 FPS )  1280 x 720 , AA : off , 60000 ms

Catzilla Benchmark
htt p://imgur.com/Gh96GPT

Bimmerfx
Sajin, I'm up and running!... Greatly appreciate the help. 
I ran the 1M Plasma Particle Benchmark from EVGA,,, I'm not sure of how good the score is.
Score 16721 points ( 272 FPS )  1280 x 720 , AA : off , 60000 ms

Bimmerfx
Vlada011, How did you get 2 GTX cards to work in SLI with a Z800.  I was told SLI would only work in a Z800 with Quadro cards. 
Thanks

You didn't understand... I have i7-5820K, X99, DDR4 and GTX780Ti K|NGP|N.. she is 200 MHz overclocked boost on 1215MHz and because of that are all results few percent better than GTX780Ti... That's nice to see. When you see somewhere GTX780Ti result you run benchmark and always you have better score...
Higher graphic score, faster rendering,... Except if you check with some watercooled overclocked card for benchmarks... But I play games on same clock.
But now K|NGP|N cost a lot. I payed premium GK110 full unlocked, that's best Kepler chip, K|NGP|N version only 760 euro... Now you can't find reference GTX1080 for that price in Europe... Maybe you can find some GTX1080 for that money... You see how much NVIDIA Increase prices. And we complain in that time how much they ask 760 euro for premium... Look now. For 3 years who want to play games will need to pay 1000$ not for premium or high end... Only for some decent graphic card to play games without filters. 
 
People usually think we will buy some cheaper card and overclock on K|NGP|N clock and they show score from benchmark tests as evidence... But real thing is if you can play games on same speed as highest overclocked model. That's little harder and nobody think like that. They are ready for gaming on such high clock not for benchmark tests only.

GK110 - TITAN, GTX780Ti, GTX780 and TITAN Black could work in Quad SLI together.
For you maybe is best if you can find TITAN with 6GB or TITAN Black. 
I think TITAN Black could be bought for 250-300$.
 

I have a large scene in Blender and it still seams to be running slow and freezing. I dont believe i should be having an issue. Maybe its a driver issue... i will try another driver... is it ok to just update or should i clean install...what is the best program to uninstall graphic card drivers?