My hp 8510p keeps overheating when i run an application that stresses the gpu. the fan is working fine and i recently applied thermal paste twice to no effect. i cant run games that i was able to run

Applying thermal past should be as small as a match stick head (about 3 should do the trick.....does for me all the time).

A zinc or copper based thermal past will do just fine. Sodium fluoride which is found in almost all toothpaste..works for me as well.

As for the pressure as soon as the heatsink sites and locks that will do just fine.

You are correct. The machine will shut down or Blue screen if it over heats. The over heating can be caused by the Heatsink on the CPU or GPU not providing a good enough heat conducting channel for cooling. Cleaning the fan is a good start, but also be aware of where the PC stands, is there sufficient ventilation for example to extract the hot air?
Being an All -in-One will make more difficult. But check if all electrical connections are secure as the power supply can also cause your machine to shut down and the power supply fan should also be cleaned.
To apply Thermal paste you have to dismantle the machine and get to the Motherboard. I suggest you take it to a repair centre as the dismantling can be difficult in these units.

A) FOLLOWING Anti-Static Procedures;

1) Clean the inside of the computer out

2) Replace the Thermal Paste on the Processor (CPU)

THOROUGHLY clean top of CPU (Processor), and bottom of Heatsink.

PROPERLY apply fresh, new Thermal Paste.

http://www.hardwaresecrets.com/article/274

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3071621&CatId=503

http://www.dell.com/support/Manuals/us/en/19/Product/optiplex-gx620

Click on the blue ->
Dell Optiplex GX620 System User's Guide (5990KB)

Using Mini Tower Computer as an example;

In the list click on;

1) Removing the Computer Cover

2) Processor

For additional questions please post in a Comment.
Regards,
joecoolvette

Could be due to the system overheating; does it run hot?
Try using it on a hard flat surface to see if it runs better, allowing better airflow around the machine and check the fan is running, you should be able to hear it.
If it's overheating, it will shut down to prevent heat damage. Overheating can be very destructive to pc components. You'll need to open the case to get to the heatsink, fan and vents. Remove the fan and heatsink and clean. Clean all the vents with vac or compressed air. Apply a little thermal paste to the processor and replace the heatsink and fan.

Silicon will bridge the gap between the CPU and the heatsink, but this will not have any thermal transfer properties. You should first of all see why the heatsink and CPU did not meet and why there was a gap. Under the heatsink and on top of the CPU there should be thermal grease, and above the graphics chip, there should be a thermal pad, it looks like a blob of blu-tack, if this pad is missing, it will not allow heat to transfer between the graphics chip and the heatsink and eventually destroy the chip through overheating. if you have got this working using silicone, you will find it does not last for long. If it is shutting down now, it is due to overheating

I'd strip the laptop down, find out what is causing the heatsink not to sit firmly on the chip (is this the right heatsink and fan for this laptop)? Clean and regrease the chip and area on the heatsink on which it sits and gently tighten up the spring loaded screws in sequence.

Clean off all the silicon and make sure there is a thermal pad on the graphics chip (may also be one one the southbridge too)

Your laptop is presenting a GPU overheat witch is consistent with the horizontal lines coming from the video card output, thus it shuts down to prevent damage. Let me tell you how I know this I recently a year ago fixed a unit with this same problem on youtube.com/rulds2008.
You can got to my laptop repair video there. What I did was not easy, I had to take apart the laptop as a whole. I cleaned out the fan units witch is connected to the same heat sync the cpu/gpu is connected. I put some thermal paste on the gpu chip.
I put it back together and the unit lasted another year or 2. The issue is within the manufacturing of this Hp laptop witch caused this problem to begin with. The manufacture used some thermal sticker that was put on the gpu that wore off thus the gpu got hot.
A overheated gpu causes damage, if your unit was damaged then a motherboard replacement will be in order. I clock a motherboard replacement at $230 bucks. You might want to check ebay.com tho if you decide to go that route. A temp fix is thermal paste on the gpu itself.
I work for your ratings, So if your inclined to watch my videos, and choose to try what I have done please let this be at your own risk, I been in the repair biz for a long while. Please do not forget to give a feedback rating.
Thanks and best regards,
Rulds2008 "ED"


Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/edwy_1a56970cf1ea4620

EDIT:

the problem is the nVidia GPU. it often overheats. there was a recall for this computer a while back. the recall has ended, but just so you know, you need to find a way to better cool the GPU. a copper shim between the GPU and the heat-sink will do wonders for you. apply Arctic Silver Thermal Epoxy to the shim and attach it to the heatsink. then, you need to use arctic silver 5 thermal paste on the GPU (about .2 grams should cover it) and reattach the heatsink to the board. while you are at it, replace the CPU thermal **** with the as5 thermal paste. my GPU is running now between 58 and 66 C. its really high still, yes, but the computer will not longer shut down because of overheat. get a laptop cooler for this thing too. it will not survive a hot summer day. i am absolutely positive.

This model of laptop has an overheating problem. This problem affect the Nvidia GPU and cause that issue. You have two options, one cheap and one expensive.

The cheap one is that you must overheat the Nvidia GPU, in order to resolde it again. This procedure you can make it with a Heat Gun. I mean you need to extract the motherboard and apply the heat directly to the GPU 90 seconds max. Put all the pieces together again (dont forget to apply thermal paste to CPU and GPU) and when the laptop turn on again, go to the HP website and download the las Bios update to your model.
This solution give you as long time as you work with your laptop fresh. You can download the CORETEMP application, to keep watching the CPU temperture.
Cost: $ 20 Heat Gun (harbor freight), $ 7 new thermal paste (for the CPU and GPU)

The expensive one is send your computer to a authorize service center and ask for a reballing repair to your GPU. Cost may be $ 200.

If you need more details, let me know. GOOD LUCK

Although you have re-flowed the motherboard and applied thermal paste, it is unlikely re-applying the thermal paste will fix the overheating problem in this case. All I can say is that you made sure the thermal paste layer was very thin, and was in between the CPU and GPU and the heat sinks. It doesn't matter if you put paste on the heat sink or the CPU/GPU, as long as it makes a good contact between them. Too much paste will have the opposite effect of cooling as it actually acts as an insulator when the layer is too thick. Do not try and get the heat plates off of the CPU/GPU as you will probably cause more damage than good. Try it once more with a very thin even layer of paste between only the CPU and GPU and the heat sinks and see if it helps. If not, don't just bin the console! Even in its current state you can sell it on ebay for up to £100. The 60Gb consoles are very sought after due to their backwards compatibility and if the blu ray player is still working then that is even better!

Hope this helps and thank you for using FixYa

Your console is overheating. It needs to be disassembled and new thermal paste applied to both the CPU and GPU processors and it will be fine.