Power supply and motherboard connections not consistent

JeffKaplan

Prominent
Apr 23, 2017
1
0
510
So I've been in the process of building my first PC. Currently missing a graphics card but I thought I'd get everything else ready to go. Got everything wired up and plugged in my power supply and.... nothing. Being my first PC build I wasn't sure what to expect. So I took a look in and consulted my manuals and everything is how it should be. So I tested the power supply with a testing device that came with it. I took the 24 pin plug and connected it to the testing device and sure enough the LEDs and fans in my PC turn on. So I try again inserting the 24 pin plug into the motherboard while doing this I notice that while I have the PSU plugged in and on, (Not great I know) but as I insert the 24 pin plug the lights on the motherboard briefly turn on as well as my PC fans and processor fan. So I know both the PSU and motherboard work to an extent but not when plugged in to each other. What I cannot determine is why does it not stay on when the plug is fully pushed in. Any ideas would be helpful.

My PSU and motherboard:

PSU: EVGA 700 B1, 80+ Bronze 700W

Motherboard: MSI 970 GAMING DDR3 2133 ATX AMD Motherboard