PC turns on and off with no display.

[Alexed]

Hello,
So my issue is that my PC was working well before with everything working correctly, this morning I had to change the thermal paste for my CPU because it was overheating and after everything is done I got everything back and turned on my PC, all the LED lights are on, the fans are turning but it turned off after about 2mins and no display on the screen.

 

[Sedivy]

Are you able to get into bios? Or never even get that far?

 

[Alexed]

Nope I'm not able to, no display on screen.

 

[Sedivy]

Which cpu model? Does it have integrated graphics?

 

[Alexed]

I have the i7 4770.

 

[Sedivy]

Ok so integrated graphics should kick in once you remove your gpu. Open your case, take out your gpu, then try to start the system and see if you get display showing.

 

[Alexed]

I did that and it still doesn't display anything, note that it still turns off after 1 mins with everything on PC working.

 

[Sedivy]

Oh...no image at all with integrated graphics? Ok. What connection to the monitor are you using? dvi? hdmi? can you change whatever you're using for a different kind and check if any change? Get a different cable if you've got it. Can you confirm on another computer that the monitor is working ok?

 

[Alexed]

Yes the monitor is ok and I'm using a DVI cable.

 

[Sedivy]

If you're absolutely sure it's not your cable then it's unlikely that both your dvi on your mobo (I'm assuming you did switch the monitor connection to the mobo when you took out the gpu right?) and dvi on your gpu is down at the same time.
It could be your cpu since you do mention that you've changed thermal paste so the cooler might not be sitting right in which case it overheats quickly but you'd get some sort of display at least. If you've nudged cpu during thermal paste change, maybe one of the pins got bent? Check the cpu carefully for bent pins but I would have expected it to not wait 2 min then in order to turn off. Still check.
Otherwise it comes down to your mobo or your psu. If you want to check your mobo, do part 2 of this test: https://www.wikihow.com/Check-a-Power-Supply
Mobo you'd have to take into repair shop (and psu if you don't have the voltage meter to do the above test). Maybe you static shocked it when changing the thermal paste.