Question CPU possibly causing power cycle?

[Saus_sarge]

Afternoon guys,
Wondering if any of you awesome people can help me here....
I upgraded my partner's rig as he wanted a new GPU, but needed a bigger PSU as well. Long story short, case wasn't big enough so installed PSU into old case and rolled with rest of old system...
Intel i3 4170 CPU lga1150
Msi z97 gaming 5 mobo
20gb ddr3 ram
Win10
240gb ssd as boot drive
Msi gtx750ti GPU
CM850x psu
On installing the new PSU, the pc power cycled twice and then booted fine. Partner was able to game for 4 hours that day and for the entire following day no issues.
Day 3 new case arrives, so I install everything into new case...
Pc won't boot, mobo lights up, fans spin, HDD and ssd seem to be working, monitor picks up a feed but no boot just black screen.
Checked forums and Google, suspect mobo as problem. Buy new mobo. Install everything again and still nothing, same as above.
So now system build is as above but with rtx2070 GPU.
Tried known working CPU (i5 4670) in said build and it powered up fine, no boot issues etc.
Tried CPU in known working build (my rig) and pc begins to power cycle.....
My rig is a
MSI mobo z97 gaming 5
Msi gtx 750ti GPU
Win10
240gb ssd to boot
CX650 PSU
I've had no issues with this rig til I tried that cpu in there. I've rest CMOS etc, tried breadboard etc. So now I'm beginning to doubt it is the mobo? Could it be the CPU? If anyone has any suggestions I'm all ears.....

 

[Saus_sarge]

Ok update to the situ...
I noticed something on a forum about booting with 1 stick of ram, so I've tried.
By having 1 stick out of my two (that were working fine before I tried this cpu) in slot 2 of the mobo it boots fine, as soon as I try my second stick in any other slot, it power cycles.
I'm totally lost as I know all parts are working and have worked prev. Yet won't now work.