https://www.pcgamer.com/5-fixes-when-your-pc-randomly-wont-turn-on/

PC Gamer is going back to the basics with a series of guides, how-tos, and deep dives into PC gaming's core concepts that we're calling The Complete Guide to PC Gaming. There's much more to come, and it's all being made possible by Razer, which stepped up to support this months-long project. Thanks, Razer!

We already covered some of the common reasons why a newly assembled PC might not boot, such as plugging in the front panel connectors (and specifically the power switch) incorrectly and missing motherboard standoffs. If you’re having an issue with a new build, you should definitely check that out. However, it’s not always brand new PCs that can be problematic.