(Some random color)SOD while USING computer normally

I have a Dell L502x. About 4 months ago (and still happen now), my computer just give me a single colored screen and lock up like this picture. In that case, it's pink, sometimes it give me other colors like black, white, green,... just a plain screen without information and the fan just rev up. Restarted the computer and a few minutes later it happens again. Sometimes it can stay up for days, sometimes it just a matter of minutes. I was using Windows 8 and keep getting that, so I went back to Windows 7, still happen! One time I don't use the external monitor, I can see the bsod (maybe it cannot output the bsod to external monitor?) error regarding Nvlddmkm.sys. I tried running the Diagnostics but it said no dump found although I have already followed the guide to make complete dump (running the .reg file). But anyway, I have attached the folder with this post. I hope somebody can help me.

At first, I thought my computer was overheating, I disassembled it and cleaned up the fan and components, but it still happens. I ran CrystalDisk and I found this: Picture. Is it bad? What's wrong with my computer ...

Test your RAM modules for possible errors.
How to Test and Diagnose RAM Issues with Memtest86+
Run memtest for at least 8 passes, preferably overnight.

Stress test the Graphics Card using Furmark.
Video Card - Stress Test with Furmark

Let us know the results. And, are you within warranty?

Nothing is bad in it, apparently.

Hi ppkhoa,

Since the issue duplicated after you migrated from Windows 8 to Windows 7, it does not appear to be a software related problem.

Your system has an older BIOS version (A9). Try flashing the latest BIOS and check results.
Note: Before flashing the BIOS please check the following: Battery should have 10% or greater charge; Adapter should be connected; No external devices should be connected; All other programs should be closed and documents saved.
- Click http://dell.to/15KdW2P to download the latest (A11) BIOS version. Follow the on-screen instructions to follow through with the installation.

Arc has correctly suggested you with the Memory and Video Card diagnostics. The test are likely to produce some decisive results. Apart from these tests, I would suggest you to run the built-in system diagnostics also. The on-board tests scan all internal components and may also produce conclusive results.
- To run the diagnostics (PSA - Pre Boot System Assessment), you may refer to the following article: http://dell.to/ZxQoxc

Do reply with the findings. We will take it forward from there.

Okay, so here's what I did: I updated the BIOS, ran the MemTest, I took a picture of the screenshot here. Also, when I ran the Furmark for Graphics Card test, I let it run for a while, it doesn't seems to cause any crash or error. Look here. I took that picture a little early, I let the test run for another 25 minutes, the temperature still maxed out at 95oC and the statistics is just like what you see in the picture, except the time is more. After that, I play SimCity for a while (4 hours) and then it give me this and my computer just lock up like I said in the first post, the color this time is different than the last time. I have attached the new diagnostics with this post.

Note that I have already chose to only display on external monitor, the laptop monitor is still on (don't know how to turn it off, I used the Dell touch button, next to the WaveMaxx Audio button to turn the screen off but it's only turn the external monitor off)

Edit: I have run the PSA and here's the result. It asked me if I want to continue after the first few tests and says it may take 30 minutes or more, I chose yes and the screenshot is the result afterward. After I restarted my computer after PSA, I got another color screen

Hi ppkhoa,

Regular system crashes can get frustrating. Troubleshooting such issues may take a while as we diagnose and narrow down to isolate the root cause. Please be assured; will ensure that we reach a conclusive foreground as soon as possible. Thanks for being co-operative.

The diagnostic tests do not point at any hardware issues so far. I recommend you try re-installing display drivers in the correct sequence to see if that helps. 'XPS L502x' is shipped with 'Optimus technology. The currently installed drivers in your system do not appear to be the OEM drivers. Would suggest you to uninstall the display drivers (Intel and nVidia) and re-install fresh set of drivers from Dell support website. Please refer to the following article to find detailed steps and the recommended sequence: http://dell.to/14tZ3Sj

Note - To install fresh drivers, use the links shared below.
To install drivers for Intel HD Graphics 3000, click http://dell.to/12lxI6k
To install drivers for nVidia GeForce GT540M, click http://dell.to/11yAgJp

After both drivers are installed, follow the steps listed in the following tutorial to switch displays between the laptop and monitor: Presentation Mode - Change. 'Projector only' mode is likely to result in display only from the external monitor.

Observe the system performance to see if it crashes again. Do reply with the findings. We would be glad to assist.