Question ASROCK Z68 pro3 system boots but nothing on monitor please help

[malibu200786]

So I've been messing around with slight overclocking this is my first time I was watching YouTube on how to do it . And set everything lower than they did to start with.
Motherboard is ASROCK Z68 pro3 with i5 2500k .
I took it 4.2ghz but on burn test was going to past 80oC so stopped it and went down to 4.0ghz .
Everything was working fine . Then Nvidia ask me to update the game ready drivers for my GTX 1050ti which I've done .
When my son was playing GTA 5 it kept crashing the pc .
Then after the 3rd time it won't come back on

 

[Tom_nerd]

try booting into safe mode. that will discard all overclocks

 

[Tom_nerd]

also try adjusting the CPU/GPU votage if it is crashing that's normally why PC`s crash after being overclocked.

 

[malibu200786]

also try adjusting the CPU/GPU votage if it is crashing that's normally why PC`s crash after being overclocked.

Thanks for reply but how do I boot in safe mode when nothing comes on the screen ?
I also tried taking graphics card out and plugging VGA to motherboard still didn't work .
I then tried the CMOS jumper and battery still nothing .
What is happening is I press the power button , the fans will spin the led lights on the fans and case will be on the CPU fan and graphics card are spinning . But nothing else happens on the screen , the keyboard lights don't come on or my usb WiFi dongle doesn't light up ?
How can I tell if it's the motherboard what's broke or if its processor?