Hi and welcome to the forum
Yes, with custom-built we need FULL hardware specs
to help you further. Make/Model of your Motherboard, CPU chip, GPU chip/card, RAM Make/Model/Specs, BIOS version, and PSU Make/Model/Wattage.
The first thing to do is to try another keyboard and mouse that works on a different computer either that you have or from a friend, family member, co-worker, neighbor, etc. AND
make sure that the keyboard and mouse you borrow from that other computer are NOT WIRELESS!!
Make sure they are BOTH WIRED DEVICES!!
Troubleshooting with wireless peripherals often leads to unpredictable results due to low batteries, bad Wi-Fi signal from keyboard or mouse, interference from other wireless devices in your home such as portable land line phones, microwave ovens, fluorescent lamp at your desk, etc. etc. If the keyboard/mouse you are borrowing for testing works, then either your wireless keyboard and/or wireless mouse are broken and must be replaced!!
Next possibility is if the above test fails using a wired keyboard/mouse with your computer. You have something seriously wrong with your computer hardware. To test this theory, access your Motherboard's BIOS using keystroke combo such as <esc>, <F1>, <F2>, <F5>, or <F10>, see your Motherboard Owners Manual for which yours requires. If the wired keyboard/mouse still do not work in the BIOS, you need to power off your computer, crack your case and disconnect the hard drive. Repeat the test. If the wired keyboard/mouse works now, your Hard Drive has failed and must be replaced!
If the keyboard/mouse still fails even with the hard drive disconnected, the last test you can make is to REMOVE ALL RAM STICKS
from the Motherboard, and repeat the test with the wired keyboard/mouse. The computer won't boot at this point, you probably won't even get a splash screen for your Mobo (ASUS, Gigabyte, etc.), but you should hear "Beep Codes",
which are short or long audible tones coming from your PC speaker or the speaker on the Motherboard. If you don't get these, most likely your Motherboard is borked, and you need to replace it!
Accessing the BIOS with your wired keyboard/mouse removes all instances of W10 or any other windows from being involved in the problem, as does removing the Hard Drive. If you can get no activity with a wired keyboard/mouse without the Hard Drive attached (containing W10), you are very likely looking at one or more failed RAM Sticks or a Mobo failure. The step above, removing all your RAM sticks, listening for Beep Codes, is the last step in the troubleshooting process--no Beep Codes! Time to replace the Mobo--it has failed!
Many times, users only use whatever keyboard/mouse they have on hand, and these days it's one or both wireless devices. However, any good tech will tell you there are a dozen ways those devices can fail internally that have nothing whatsoever to do with Windows, and therefore you must go back to the "old school"
method of troubleshooting with wired devices like we used to do back in the 80s & 90s.
This should narrow down your problem for you. <<<<BIGBEARJEDI>>>>