ASUS mobo, Dell monitor, HDMI, no BIOS menu, white light on

Updated: November 20, 2020

The title of this article sounds like nonsense, but it is actually a recipe for a weird problem I've encountered with a desktop system. As it happens, it's a custom-built PC with an ASUS motherboard. The computer monitor is made by Dell. The two devices are connected using an HDMI cable. So far so good.

Then, I had the system rebooted - after months of calm and peaceful work - and during the boot sequence, the following happened. The screen went into a sleep mode - the usual no signal from HDMI. Then, it didn't wake up right away, so I didn't see the BIOS splash (the whole press F2). Then, the LED on the motherboard cycled through the color sequence - red, yellow, white, green. Nope, no green. The white light stayed on.

There are four lights!

So, I went online and consulted the motherboard's manufacturer site, including the indication of the color code and possible errors. As it happens, the white LED on indicates: display connectivity problem. Well, yes, because I can't get into the BIOS. However, once the boot sequence completes, the system works fine - the monitor wakes up, you can log into Windows and whatnot.

We have a problem that seems to be ... partial in its effect. But then, for several months beforehand, plus several reboots, there were no white light issues. Does this mean we have a hardware thing? Well, I set about troubleshooting, one cable at a time.

DisplayPort versus HDMI

The Dell monitor ships with the DisplayPort cable (no HDMI). I figured, well, if this is what the vendor giveth, then let's see if that somehow affects the situations. I changed the cables, rebooted, and poof, the white light was gone. It blinked, system check, good, green light - and the sequence finished successfully.

However, there was still no BIOS - the monitor would not wake at the right moment to show me the motherboard logo, and allow me to press F2 to get into the BIOS settings.

Monitor drivers

It seems that using a different connection type solved half the problem. But the issue of the monitor's so-called "deep sleep" remains. I decided to try something else. I powered down the system. This time, I did get to see the BIOS menu. But then, following ANOTHER reboot, nope.

I realized that I needed to focus on Windows 10 and how it handles power management. After all, when the operating system goes down, it sends a bunch of signals to the connected hardware devices. Apparently, something causes the Dell monitor to sleep, and then not wake up at the right moment.

I checked the device properties - and realized that the monitor wasn't recognized as Dell. Nope.

Generic monitor notice

Now, the monitor was behaving fine - the color calibration, resolution, refresh rate, sleep, all of it. Inside Windows, there were no issues. But then, it was also categorized as a generic device and using the standard Microsoft drivers. I figured, let's see what happens if I try the official Dell drivers.

Monitor drivers

I installed the drivers, and then power-cycled the monitor (off, on). Now, the Windows 10 device manager was showing the device correctly - Dell U2719D. Excellent. I rebooted the system, and now, the entire sequence went smoothly. The lights did their flash dance, the BIOS menu was there, all of it. Problem solved.

Conclusion

This article may not be relevant to too many people. But I think its message is important. I had to solve a problem that manifested suddenly, despite having introduced no system change, a problem that doesn't really have any "crippling" effect on day-to-day usage, a problem that seems to be a mix of two components, hardware and software, never fun.

In a way, software is quite fragile. Subtle differences among components in a near-identical setup can make a huge amount of difference. You could have a system that works perfectly, and then a different system that does funny things, and it comes down to a single cable or a driver. I mean okay, but there ought to be more resilience.

Anyway, enough philosophy. If your mobo lights go blink on you, and the data points to a connectivity problem, try to work your way through methodically. Try to isolate the issue by working through the different setup permutations, stick to the defaults where possible, because that's what vendors usually check to certify their hardware, and make sure the drivers are configured correctly. Sounds trivial, but it's not when one little light suddenly switches on and starts annoying you. Hopefully, this will be of use, if not as a straight howto then as a generic and practical pointer. Bye bye now.

P.S. The SMPTE color bars thumbnail used on the homepage is licensed under CC BY-SA 3.0.

Cheers.

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