PC randomly restarts but not while under load

[dethsight]

i've had my build going fine for a few months now. it hasn't really given me any trouble so far, but in the past few days, its decided to reboot itself while i wasn't even doing anything with it. and it wasn't a windows update. i made sure i was all up to date before this last reboot. no error screen. no blue screen. hasn't crashed during benchmarks or gaming...etc. any info would be great. specs are below

 

asus zenith extreme X399 bios v0503 (i think. whatever one had a 5 and a 3 in it)

threadripper 1950x at stock speeds

gigabyte aorus 1080Ti 

corsair HX1000 PSU

corsair vengencae ddr4 ram at 2666

samsung evo 500gb and 250gb m.2 drive

samsung evo pro 1TB SSD

enermax liqtech 240 AIO

bequiet! dark base pro 900