Can't start up computer

[SOMETHING]

I was taking my computer out of its case to clean it and test out some new bits of hardware and when I took it out of the case I had to take it apart. When I put it back together out of the case I couldn't get it to start. I'm a complete novice when it come to computer hardware so I think iv just misplaced a wire. And comments would be extremely helpful.
https://youtu.be/gESdmsQJSZU

[patio]

I'm not gonna watch a video...double check all your connections with all power removed to the PC.

PS how did you clean it ?
Don't say vacuum....

[SOMETHING]

I have gone through all the connections. No I did not use a vacuum.

[patio]

Remove any new hardware you added to test...

[Rustys]

You took it apart did you remove the heat sink form the cpu?

If so then did you remember to wipe the old thermal goop off and replace with new.  Since it is outside of the case what is it sitting on?

[SOMETHING]

I didn't take the CPU apart and it's currently sitting on my desk

[chaosloader]

Did you put and verify all your power switch pins are correctly connected or not...

That might be the issue...



P.S
to correctly connect them I think there will be layout on the motherboard

[Lorraine walsh]

Try testing the CPU fan to make sure it's functional, if it isn't it could prevent a POST.

You also need to make sure all the case connections are correct. Power switch and power reset especially.

Did you look under the MB for any loose screws or other short hazards?