Help !!!Dell Inspiron 17R 7720 SE won't turn on after cleanup

So I won a Dell Inspiron 17r 7720 SE since 2012. Service Tag . Recently I encountered problems with the Nvidia GPU 650m . I was not getting detected by my pc.Even the latest official drivers won't recognise it.So I concluded that a cleanup of the inside would solve the issue.Moreover the laptop was also running quite hotter.So last night I took apart my laptop following a video guide from PartsPeople.com cleaned it up with rubbing alcohol ,replaced the thermal paste with Arctic Silver compound.And put it back.Frankly it was easier than I thought.But after everything the laptop won't turn on.There's nothing ...no beeps,no less nothing .It's just dead.

Hi SOUMYAD.999,

Download the service manual here if required - http://dell.to/2dgKV7V

Open the chassis and check if you have connected all cables properly. 

Remove the memory modules / HDD / ODD and check if the system responds.

If nothing works, then I would suspect a motherboard failure.

You would need to replace the motherboard and fan assembly / heatsink.

You could order the parts from parts-people or contact our team to get a quote for a paid service call - http://dell.to/1vnT6CQ

Let us know if you have any other queries.

Well there has been another development.At first the laptop was totally not responding,but yesterday I saw that the led for battery is on when I plug in the ac adaptor.Its not turning on though.But is there a slightest chance that it may revive.

And thank you for the previous​ speedy response

Hi SOUMYAD.999,

Were you able to disconnect the memory / HDD and check if it responds?

Let us know if you have any other queries.

Recently I encountered problems with the Nvidia GPU 650m . I was not getting detected by my pc.Even the latest official drivers won't recognise it.So I concluded that a cleanup of the inside would solve the issue.

I recently had a system on which the Nvida GPU failed three time requiring a motherboard replacement.  The system was eventually replaced and the GPU has not failed since. 

Since you say you did a "Cleanup", what exactly did you do?

Hi SOUMYAD.999,

Thank you for the update.

With all those components disconnected, have you tried to power on the system and check if it responds? Ideally, without the memory installed, if the system does power on, it will detect the absence of memory modules and indicate the same with beep codes.

As advised earlier, if nothing works, the motherboard needs to be replaced.

Let us know if you have any other queries.

I have this exact same issue, but it's a little stranger.

The strange thing is that this first happened over a year ago.(Reference: en.community.dell.com/.../19651693 )

No response from the power button at all, BUT the battery was clearly charging. It really seemed like a bad power button. I disassembled and reassembled it a few times (I'm an IT guy), checked every part, replaced the button battery, etc... Tried all the steps suggested above as well, including booting with no memory or peripherals to try to get beep codes. NOTHING. Before this, the laptop was fine. No over heating, no crashing, etc... I assumed a bad power button, because power was clearly flowing through the motherboard (and charging the battery).

Here's the shocker: before I got a chance to order a new power button, it just started to work again. It wouldn't boot, wouldn't boot, wouldn't boot... I kept it on my desk for a few days while I was deciding whether or not to order a new power switch or motherboard, and one day while walking past I pushed power and IT BOOTED.

After that, it worked fine for a YEAR AND A HALF! Never crashing, never failing to boot. Standby worked, etc... Flawless for 1.5 years.

My guess was that the power button ribbon cable wasn't making a good connection but that it finally seated properly, or a finicky capacitor released it's charge, I don't know...

Then about two weeks ago I tried to boot it up again, and AGAIN it WON'T BOOT.

This time I didn't wait and ordered a new power button. Sadly, that didn't fix it. Battery charges fine, but no response from the power button at all. Power adapter light stays on properly too, FYI.

I'm tearing my hair out over this. It really seems like it should boot up!