At the work I wanted to have some computers boot automatically when triggered over WakeOnLan. There are four computers with the exact same specifications (HP Compaq 8200), but on three of them, when triggered by WakeOnLan, they would only display a blinking underscore instead of booting Windows.
This problem was already reported on various sites but had no official solution:
When analysing the difference between the working and not working setups I noticed that on the working computer the disk was using the MBR (Master Boot Record) to boot and the three not working ones were using GPT (GUID Partition Table).
MBR is the old legacy way and GTP is the newer UEFI way of booting a system. As a next step I looked if there were any updates for the BIOS of those systems that could maybe fix the problem.
I found a newer BIOS and installed it on one of the machines, and it worked. With the new BIOS in place it booted correctly into the Windows Installation.
Another worse way of fixing it would have been to convert the GPT to the MBR format, but that wouldn’t have made much sense and would lead to probably more problems down the road.