Why is my laptop not turning on?

Question

HP EliteBook 840 G3

Repair information for the HP EliteBook 840 G3. This Hewlett-Packard laptop is designed for enterprise usage.

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Laptop Model: HP EliteBook 840 G3 (Energy Star)
OS: Windows 10
SSD: 256GB NVMe
RAM: 16GB

After a recent Windows 10 update (auto-installed overnight on 10/09/2025), my laptop no longer boots properly.

When I press the power button:

Power drain reset – Held the power button for 30 seconds to discharge. No change.
Battery removed – Tried running only on the adapter cable. Result:
- Power and Caps Lock blink once, then system shuts off, looping again.
CMOS reset – Removed and reinserted the CMOS battery. No effect.
RAM reseating – Swapped RAM modules into different ports. Problem persists.
BIOS recovery attempt – I already have the correct BIOS flashed onto a USB drive, but the system doesn’t stay on long enough to start recovery due to the boot loop.
Pending test – Planning to test with a different RAM stick to rule out memory failure.

Laptop is stuck in a boot loop, unable to load BIOS recovery or Windows.
Only remaining suspected causes: RAM issue, motherboard fault, or BIOS corruption.

Anyone with the same issue and successfully fixed theirs?

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Jelly Bean man @jellybeanman crwdns2934065:0crwdne2934065:0: 906 12 1 · Answer 1 · 2025-09-17T03:09:35-07:00

It powers on, lights flash, HP logo shows briefly, then power-off loop →
Not a dead motherboard (since you get the logo), but the handoff between firmware → POST → OS is failing.
Caps Lock flashes once →
On HP laptops, blink codes matter. A single Caps Lock blink is usually CPU not functional or BIOS corruption, but since it gets to the logo, CPU is probably fine. This points more toward firmware/BIOS corruption.
Windows update before issue →
Sometimes HP BIOS auto-updates via Windows Update (yes, really). If it failed or glitched, it leaves the system in exactly this loop.

Plug in AC adapter.
Hold Windows + B keys, then press and hold the Power button for ~3–5 seconds.
Keep holding Windows + B until the screen lights up or you hear beeps.
This forces the system into HP BIOS recovery mode from USB or internal recovery partition.
Since you already prepped a USB with the BIOS, this is the method most likely to get it working.

(If Win+B doesn’t work, try Win+V instead — some EliteBooks use that combo.)

You mentioned you’ll try this — good call.
Boot loops with a quick logo flash often happen when RAM partially works (detected but failing during POST).
If you’ve got spare DDR4 SODIMM, even better for cross-test.

If BIOS recovery doesn’t kick in:

You’d need an external programmer (e.g., CH341A clip) to reflash the BIOS chip directly.
This is usually the fix if the system bricks after a Windows-pushed BIOS update.
Not DIY for most, but repair shops can do it quickly.