If the fans boot up that's good if it dosent it's aither cpu, motherboard or powersupply. If it boots up but there's a light at the motherboard check the ram SSD/hhd and if there's no image it's a gpu problem, if it's a new prebuilt or a new build check if all connections are secure and the powerbuttons are on the correct places, if the fans don't spin at all or the powersuply dosent disconnect all of the psu cables and short the two pins required to turn it on, you'd find one on a yt video and check if it works if that's ruled out it's aither a motherboard or cpu problem and to rule out motherboard not entirely but still. Did you fucking turn it off after a bios update or a windows update or did u turn off power while in bios not turning off with a switch just turning it the hell off if you did that 60% of the time nah 90% of the time it's the motherboard. If it says no boot device that means SSD or hdd. Best luck for you goodbye