Display turns black on starting ANY game.

[rathod.aryan.2001]

(I dont know under what category my query exactly fits into)
I built this system in march 2015 and it was working till yesterday. I recently bought a new case (s340) and shifted all the parts into it.
My pc seems to working just fine (I can perfom simple tasks) but crashes almost immediately when I start any game on it. The screen turns black and the monitor shows -"no display"; the pc still seems to be running with all the fans spinning(The fans dont freak out neither they go to 100%).
Again this happens only when I start playing any game.
here are my pc specs -
Windows 10 home 64bit (updated some weeks ago)
i7 6700 (non k) antec AIO cooler
gtx 970(asus strix)
asus h170m motherboard
8 GB RAM
750 watt power supply
128 GB SSD
1 TB HDD
I scanned and repaired
I did install every component properly, changed the thermal compound and cleaned every component before the transfer. I did use proper methods to clean said components. This is really freakin me out! Please help!
P.S. this is my first using this website

 

[alceryes]

Did you move to a different power supply? Some cases come with a PS.
Did you plug the 8-pin aux power cable into the video card?

 

[rathod.aryan.2001]

Did you move to a different power supply? Some cases come with a PS.
Did you plug the 8-pin aux power cable into the video card?

I removed both of my extension cables(mother board and GPU) (just now) and then tried out.
Everything is loading properly now and I played a match of RL just fine.