What if it doesn't work?
It's a terrible feeling.
After all the time you spent planning, designing, and assembling your homebuilt computer, you push the button to fire it up for the first time...
And it doesn't work.
First of all, stay calm. And don't cry. Unless you're a little kid. Then you can cry if you want. And when you're done, start doing some troubleshooting. Here are some troubleshooting tips and tricks.
If Your Computer Won't Post or Boot to CMOS Setup
- First of all, unplug the computer from the wall and start checking connections. Almost all first-boot failures are due to something not being connected or seated properly. If you're using a fully-modular or semi-modular power supply, then make sure the wires are connected at both ends. Also double-check the panel leads from the motherboard to the case. They're easy to get wrong.
- If absolutely nothing happens when you push the power button, here are the most likely reasons:
- The computer isn't plugged into the surge protector or UPS; or the surge protector or UPS isn't plugged into the wall.
- The power supply lead to the motherboard isn't connected.
- The voltage switch on the PSU is in the wrong position, or the power switch on the PSU is turned off.
- The wire going from the header on the motherboard to the power button on the case isn't connected properly (or at all).
- If the LED's light up and the fans start turning and keep turning, but nothing else happens, here are some likely causes.
- The processor, RAM, or GPU card is not properly seated.
- The power supply lead to the GPU is not connected.
- Your monitor is plugged into the wrong port.
- You have both onboard video and a discrete GPU, your monitor is plugged into the discrete GPU, but the computer is set to use the onboard video as the boot display in BIOS. So the computer is actually booting, but you can't see anything on the screen.
- The motherboard may need a BIOS update to recognize your processor. Sometimes that's the whole reason for a BIOS update: to support processors that didn't exist when the motherboard was built.
- If the computer begins to start up, but then starts beeping (or if an LED or a bank of LEDs start flashing), check the motherboard manual to find out what the beep or LED sequence means. Most likely the CPU, RAM, or GPU isn't seated properly; or one of the fan leads (most likely the CPU cooler) isn't connected properly. The motherboard may also need a BIOS update to recognize your processor.
- If the computer begins to start up, and the fans start turning but then stop, and there are no alarm beeps or LEDs flashing, then most likely the CPU, RAM, or GPU need to be re-seated; the CPU or GPU power lead isn't connected; or the CPU fan lead isn't connected to the correct header.
- If the computer boots to CMOS setup, but BIOS can't see any of the drives, then poke for settings labeled "Drive Controllers" and make sure they're enabled. If they are, then check the data and power connections to the drives.
- If you are using both an M.2 drive and a SATA drive, and BIOS can only see one of them, then most likely the M.2 slot is on the same channel as one of the SATA headers. In that case, you can't use that SATA header when using the M.2 slot. Moving the SATA drive to another header should solve the problem. (If you'd read the motherboard manual, you would have known that.)
- Once in a while, a computer with an Active PFC power supply will refuse to power up unless it has pure sine wave power input. If your computer is connected to a UPS and won't boot up, try plugging it directly into the wall. If it boots that way, then that computer has a finicky power supply that won't work with just any old UPS. It will need a pure sine-wave UPS. And yes, they're expensive.
- If none of the above work, or if your problem isn't described, try reaching out on the Reddit "Build a PC" subreddit, or contact the motherboard manufacturer for support.
If Your Computer Won't Boot to the Operating System Installer Flash Drive
If your computer posted okay, but won't boot to the Windows or other operating system USB stick, try these steps.
- Disconnect anything except the keyboard and mouse that are connected to the computer's USB ports.
- Move the flash drive to the oldest-generation USB port on the computer, and try to boot from it again. It could be that the operating system installer doesn't have drivers for the newest USB ports. If you have a black USB port, try that one. If not, then try a blue one.
- If that doesn't work, boot back into CMOS setup and make sure USB boot is enabled. Also look for settings to enable Legacy Boot and Legacy USB.
- If none of the above work, then chances are that either your installation media is defective. Try creating a new one using the most recent available installation image for the operating system.
If Your Operating System Insists on Installing the Bootloader to the Wrong Drive
This happens sometimes when you have both an M.2 drive and one or more SATA drives. The first SATA drive is the default place for the bootloader to install; and some operating systems will install it there even if you really want it on the M.2 drive.
A related problem is when the operating system ignores the M.2 drive and simply installs to the SATA drive, not even giving you the option to install to the M.2 drive.
In either case, the solution is the same: Power down the computer and disconnect the data leads from all the drives except the M.2 drive. Then repeat the installation. This time it will install to the M.2 drive because it will be the only drive in the system.
Once the system installs to the M.2 drive, restart the computer. While it is running, re-connect the data lead to the SATA drive to which the system previously erroneously installed, delete the partition in your operating system's partitioning utility (Disk Management or DISKPART in Windows, for example), and reformat the drive.