XPS 8900, won't boot after multiple upgrades

So I started the week upgrading my XPS 8900, I purchased it in 2016 and hadn't been using it much until recent events forced me to work from home.

Original specs were i7-6700, 16gb ram, GTX745. In 2017 I upgraded it to a gtx 1050 TI with an NMVe SSD. 

I wanted to add some more power (to handle a 4k display I purchased) to it so I purchased a RTX 2070 along with 32GB of additional ram and a 850W power supply. I managed to squeeze all of that in and the system ran fine for a few hours, then crashed out of nowhere and rebooted several times with each new reboot coming sooner that the previous one, when finally it would only turn on the case fan them turn off again. After this episode, I figured given the tight squeeze, and the fact that things felt a little warm the system did not have enough cooling.

So I figured I'd try putting this motherboard in a case with better ventilation. So I purchased a new case with a total of 3 140mm fans, 3 120mm fans and a 280mm liquid cooler for the processor for good measure. I got the system to boot in the new case using tips from another post on this forum, and after one successful boot cycle where I only got the the windows login screen the system now refuses to even get to the bios screen. It will only turn on the cases fans and then restart, and then not respond to the power button. 

My concern is that I may have killed the motherboard, I tried booting without the graphics card inserted, and the ssd with no success. I also tried resetting the CMOS to no avail. 

Any suggestions would be appreciated.