[Fix] Gigabyte GA-H170M-D3H Boot Loop and Power Issues – No Display

You press the power button on a PC built around the Gigabyte GA-H170M-D3H. The fans spin, perhaps for a second or two, then everything switches off and starts again, over and over, and the monitor stays black. Or the machine powers on and simply stays dark. This is one of the most common failure patterns on desktop PCs, and you can usually isolate the cause by removing parts one at a time. This guide gives a strict order for doing that, so you change one thing at a time and know what fixed it.

The GA-H170M-D3H is an Intel H170 board for LGA 1151 processors with DDR4 memory, released for 6th-generation (Skylake) CPUs. Where a step depends on details of this exact board, such as the position of a header or the memory slot to use first, check Gigabyte’s support page for the manual and the CPU support list.

Read the symptom first

• Fans start, stop, start again (a boot loop): commonly memory, the CPU seating, a stale BIOS configuration, or an unstable power supply.
• Powers on but no display, no loop: usually memory, the display connection or graphics, or a CPU that this BIOS version cannot boot.
• Does not power on at all: power supply, power switch header, or a shorted component.

Step 1: Power and connections

Switch off the power supply and unplug it. Then check that every power connector is fully seated:

• The 24-pin ATX connector on the edge of the board.
• The CPU power connector (4+4 or 8-pin) near the processor socket. It is easy to forget, and the board will not start properly without it.
• Any graphics card power leads, if you use a discrete card.
• The front-panel power switch lead. If you are unsure, briefly touch the two power-switch pins with a screwdriver to start the board and rule out a faulty case button.

If a boot loop started right after you changed something, undo the last change first: a new part, a new cable or a BIOS update.

Step 2: Clear the CMOS

Corrupt or incompatible BIOS settings cause many loops, especially after a failed overclock or memory profile. Switch off, unplug the power lead, then either use the board’s clear-CMOS jumper or header (see the manual for its position) or remove the round CMOS battery for several minutes and put it back. Reconnect power and try again. The board reloads its defaults on the next start and may take a little longer than usual the first time.

Step 3: Strip it down to the minimum

Disconnect everything that is not needed to reach the BIOS: every storage drive, optical drive, USB device, front-panel USB, extra fans and any add-in cards. Leave only the motherboard, the CPU with its cooler fitted and the cooler fan connected, a single memory module, the required power connectors and a monitor. If you use a discrete graphics card, remove it and connect the monitor to the motherboard’s own video output instead; the processors this board supports have integrated graphics.

If the board now reaches the BIOS or the manufacturer logo, add parts back one at a time, restarting after each, until the loop returns. The last part you added is your prime suspect; also check its cable, port and seating, and remember that it adds load to the power supply.

Step 4: Memory

Memory is one of the most common causes of no-display and boot-loop faults. Try this in order:

1. Reseat the module firmly until both clips click.
2. Try one module at a time in a different slot. The manual tells you which slot to use first when only one module is installed.
3. Check that the modules are DDR4 and supported by the board. Also make sure you are not running a memory profile (XMP) that the board finds unstable. Clear the CMOS and leave the memory at default speed.
4. If you have spare memory known to work, swap it in.

Step 5: Processor and socket

Check that your CPU is on the board’s supported list, and at which BIOS version. This is a classic trap: newer 7th-generation processors can fit an H170 board but will not start until the BIOS has been updated to a version that recognises them. If that is your case, you may need to update the BIOS using an older, supported CPU first. Also look at the socket: bent pins in the LGA socket are a common result of a rough installation and can cause both a no-display fault and a boot loop. Inspect them with a torch, but never touch the pins.

Step 6: BIOS settings and Fast Boot

If you can reach the BIOS, disable Fast Boot temporarily, reset to defaults and switch off any overclocking or memory profile. The key to enter setup is usually Delete on desktop boards. Fast Boot skips parts of the hardware start-up checks, which can hide or cause problems on some systems.

Update the BIOS only if you have to (for example for CPU support) and follow Gigabyte’s instructions exactly. Do not switch the machine off or lose power during a flash, since a failed update can leave the board unable to start.

Step 7: The power supply and the board

A tired or underpowered power supply can start the fans and then fail under the slightest load, causing loops. Swapping in a known-good power supply of adequate wattage is the most reliable test. Use its own cables, or cables the manufacturer says are compatible; modular cables from a different power supply can look identical and still be wired differently. If you have tried the memory, the CPU, the power supply and a stripped-down build and the board still does nothing, the fault is probably the motherboard itself, or possibly the CPU. At that point, testing the CPU in another board, or the board with another CPU, is the only way to be sure, and it may be time to ask for help or replace the board.

Safety and good habits

• Switch off and unplug before touching any component, and touch bare metal on the case, or use a static strap, so you do not discharge static into the parts.
• Change one thing at a time and note the result. Random swapping makes a two-hour problem into a two-day one.
• Keep the case open on a non-conductive surface while testing, and be careful with the CPU cooler when you remove it, since the thermal paste will need replacing.

Common questions

Why does it loop only for a few seconds?

Because the board tries to start, fails a safety check (memory training, a missing power connector or unsupported hardware) and resets itself. The very short cycle is a sign of a failed early check, not necessarily a dead part.

Will replacing the CMOS battery fix it?

Only if the old battery was flat. Removing it for a few minutes clears the settings whether or not you fit a new one, but a flat battery can cause the board to forget its configuration and misbehave on every start.

Is it the CPU or the motherboard?

Check memory and power first, since they are far more likely. A dead CPU is rare. If you can, test the parts in another system.

Keep reading

• Windows Boot Process Step by Step (and How to Fix Each Stage) — What happens at each stage of boot.
• BIOS vs UEFI: How a PC Starts Before Windows Loads — BIOS and UEFI explained.
• PC Repair Toolkit for Beginners: What You Actually Need — Tools that make hardware repair easier.

Sources

• Gigabyte Support: manuals, BIOS downloads and CPU support lists
• Wikipedia: LGA 1151, for the socket and processor generations it supports
• Wikipedia: Electrostatic discharge