Isn't playing with a computer BIOS fun? No? Of course it is!
I'm rebuilding my main desktop system at the moment. It isn't anything spectacularly new, in fact it is based on a Athlon XP 2800+, but it runs Linux (Ubuntu 9.10 currently) with ample performance for my day to day tasks. Windows XP runs on it adequately, when it actually works (I clearly use it too little because it sulks and 'blue screens' every few months, requiring a repair or reinstall).
Anyway, as part of this rebuild I decided that it made sense to get everything bang up to date, including the BIOS. The board is obsolete now, so the BIOS was a few years old and should be stable enough - wrong! The board is a Gigabyte GA-7S748-L (GA-7S748 with on board LAN), and was running the F5 revision. Updating was simple enough, just boot of my DOS USB key (yes, I have a USB key with DOS installed!) and run the utility. This brought things up to revision F9, which was the latest, and is where things started to go wrong.
The first thing I noticed was that my Windows 7 installation couldn't see the HD, so I reached for a driver (Vista was the most up to date) to add during the install process. This didn't work, and further investigation showed that the BIOS of the PATA PCI card the drives were connected to wasn't active. It turned out that enabling USB legacy support disabled the card BIOS. Unfortunately, in order to configure the card BIOS you needed a keyboard, and since mine was a USB one, USB legacy support was required to use it - catch 22!! After trying a PCI SATA card instead I found that this was clearly a motherboard issue and not specific to one card or chipset.
So the next thing to do was to back off to the previous BIOS (F8 in this case) to see if the bug had been introduced in the latest BIOS upgrade. Unfortunately it seems that the F8 BIOS was completely bug ridden (so it is a shame it is still available for download). After installing it the computer wouldn't boot at all, although it would allow use of the BIOS itself. This board has a facility to flash the BIOS from a BIOS based utility (Q-Flash), which sounds pretty handy in this case. Sadly it didn't work, although thankfully, the failure didn't damage the installed BIOS any further. After a bit of research with Google, I found that if you disable USB support completely you can boot to a floppy and re-flash the BIOS using a DOS based utility (will DOS ever die?!).
So, with this information I managed to get back to the F5 BIOS and all was working again. Out of curiosity I then tried the F6 BIOS and found that the USB legacy support clash with the PATA card BIOS was introduced there, so presumably exists in F7 too. Back to square one again then, with the original F5 BIOS and a working PC!