Dell inspiron desktop turns on and then off

Laptop Details:

Dell Inspiron 15R N5010 4GB RAM - 500 GB HDD Intel Core 1st Gen i5 Processor 90W Power supply - Old 6 Cell Lion Battery

Known Issue with the Laptop:

The Problem

Here are the things I know:

There is no POST issue [sound] --> boot happens Not an issue with HDD --> The power down happens even if I go into BIOS and stay there for 20 seconds Most probably not an issue of over-heating -- 20 seconds seems like an awfully brief time, but I may be wrong

Things I've tried

Removing the RAM sticks and booting --> when I do this the laptop DOES NOT power off. It stays on the POST error indefinitely --> Which is surprising Removing Battery and booting only on AC power --> Same issue Removing HDD and booting --> This brings up the "Select a BOOT device" screen -- > Even from this screen the laptop powers down. Trying either RAM stick independently --> Highly unlikely that its a RAM issue

Reapplying the thermal paste - I've done this as well - no help. One caveat here - The paste I am using may be the problem, its called HT-GY260 - http

/www.amazon.com/Flashlight-Thermal-Grease-Silver-HT-GY260/dp/B00W8AJRV8. Let me know if any of you know that this is an issue.

Update:

• 
  Something I just observed - There's a distinct click sound when it powers down

Appreciate the help.

Depending on how easy it is to do this I would try detaching everything unnecessary and seeing if you still get the same issue. [Bit harder to do on laptop than a desktop]

But just leave Mobo, CPU, 1 Stick of Ram and Power cord connected, so take out other ram, disconnect hard drive, usb devices etc and see if it keeps power then. If not see if you can get your hands on an alternative power supply and try that. This does not look good though

Unplug from mains, hold power button down for 20 seconds. Plug back in and turn it on.

Have you tried resetting the CMOS? It's worth a try at this stage I guess.

Unplug from mains, hold power button down for 20 seconds. Plug back in and turn it on.

Have you tried resetting the CMOS? It's worth a try at this stage I guess.

2. How does one go about resetting the CMOS? Is it simply pull it out and put it back in? Should I consider replacing it?

It removes the power from all components, but the affect of this is that the software interfaces between the BIOS and the hardware are severed and then the BIOS reestablishes those software interfaces between the BIOS and hardware when the computer is reconnected to power. This is coupled with the clearing of the computer's temporary memory. That way, if one of the software interfaces between the BIOS and hardware is malfunctioning, it is reset. You should just be able to remove the cmos leave it out for five minutes and put it back in. Try this option second though.

Unplug from mains, hold power button down for 20 seconds. Plug back in and turn it on.

Have you tried resetting the CMOS? It's worth a try at this stage I guess.

Tried your suggestion - unplugged from mains, removed battery [is this okay?] and held power down for 20+ seconds - nothing conspicuous happened, I did not get a screen or a message or a beep when I held the power button down for 20 seconds. The power down issue remains despite this

Depending on how easy it is to do this I would try detaching everything unnecessary and seeing if you still get the same issue. [Bit harder to do on laptop than a desktop]

But just leave Mobo, CPU, 1 Stick of Ram and Power cord connected, so take out other ram, disconnect hard drive, usb devices etc and see if it keeps power then. If not see if you can get your hands on an alternative power supply and try that. This does not look good though

Depending on how easy it is to do this I would try detaching everything unnecessary and seeing if you still get the same issue. [Bit harder to do on laptop than a desktop]

But just leave Mobo, CPU, 1 Stick of Ram and Power cord connected, so take out other ram, disconnect hard drive, usb devices etc and see if it keeps power then. If not see if you can get your hands on an alternative power supply and try that. This does not look good though

Did that, same issue - I'm guessing its the Mobo. I'm salvaging the HDD and RAM, scrapping the rest. Thanks for your suggestions

Depending on how easy it is to do this I would try detaching everything unnecessary and seeing if you still get the same issue. [Bit harder to do on laptop than a desktop]

But just leave Mobo, CPU, 1 Stick of Ram and Power cord connected, so take out other ram, disconnect hard drive, usb devices etc and see if it keeps power then. If not see if you can get your hands on an alternative power supply and try that. This does not look good though

Did that, same issue - I'm guessing its the Mobo. I'm salvaging the HDD and RAM, scrapping the rest. Thanks for your suggestions

Please help out a brother

this seems to be a problem with people not asking how old the laptop is or how often its used but logic to me says to check out the powerboard containing your power button the contacts on this button could be stuck on one side thus making your laptop think you are holding the button down you can try replacing this board at your own risk but i would let a tech deal with that the other side of it is that you should test the current coming from your battery and from your ac adapter to make sure you are getting the proper and steady flow of power

Depending on how easy it is to do this I would try detaching everything unnecessary and seeing if you still get the same issue. [Bit harder to do on laptop than a desktop]

But just leave Mobo, CPU, 1 Stick of Ram and Power cord connected, so take out other ram, disconnect hard drive, usb devices etc and see if it keeps power then. If not see if you can get your hands on an alternative power supply and try that. This does not look good though

Did that, same issue - I'm guessing its the Mobo. I'm salvaging the HDD and RAM, scrapping the rest. Thanks for your suggestions

Please help out a brother

I had the same exact problem with my laptop.it would turn on for one min then shut off.diagnostics said cpu thermistor 103c.it was over heating.turns out i didnt have anymore paste/compound/heat sink left underneath my cpu.i replaced it with more,boom,problem solved! Hasnt shut off on me since [knock on wood]

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