I'm surprised, this kind of issue is really rare
What I think was happening is that the power button(or reset button) is stuck, so the computer keeps trying to restart constantly
You can buy one of these: https://www.amazon.com/SoundOriginal-Desktop-Computer-Motherboard-Supply/dp/B074891DJP/ref=sr_1_3?keywords=power+button+pc&qid=1557177689&s=gateway&sr=8-3
It should do the trick! Glad you got it solved!
I use this
I recently did a very similar build and used this button
SoundOriginal Refit Desktop Computer Case Motherboard Power Supply Reset HDD Button Switch (63inch 160cm) https://www.amazon.com/dp/B074891DJP/ref=cm_sw_r_cp_api_fab_BD0HFbM0G024D
I would drop the aimtrack guns and go with sinden light guns. I would also get a better monitor. I grabbed a 32” 1440p IPS gaming monitor with free sync for $250. Also I would get the emulator edition plus control panel if 4 way games are of interest to you.