Elenarie: Depending on which model you have... There have been a few BIOS updates, maybe one of them fixes the problem?
At that time, I was using the (then) latest G75VW BIOS, 221 (to which I had updated from the original 207). Afterwards ASUS also released BIOS 222, I've installed it too.
Anyway, with Win7, I didn't have any issues getting to BIOS, with BIOS v207 nor v221. But with Win8, I suddenly couldn't get to BIOS setup anymore (except when using "restart" instead of shutdown + power up). But when I disabled the fast boot-up option, the problem disappeared completely.
The other fixed problem I mentioned (my dual boot Win7 partition getting corrupted) was probably related to this (they are discussing about the Win8 preview, but it seems to be still applicable to released Win8):
http://social.technet.microsoft.com/Forums/en-US/W8ITProPreRel/thread/1be71590-1f43-4525-a341-26bdbccdb9df where one (MS employee?) said this:
I do want to circle back around for something related that might be hitting some of the others that were following this tread. We have come across an issue with the people that are switching between Win7 and Win8. When shutting down from Win8, the shutdown is actually hibernating. So files aren't getting closed properly. Since Win7 doesn't fully understand what happened with the Win8 shut down, some problems are seen.
For people that are dual booting, we are recommending that when they shut down from Win8, they do a 'shutdown /r /t 1'. This will ensure that they do a normal shutdown and not a hibernation.
And that indeed fixed it for me, I haven't detected corruption on the Win7 partition anymore (after I disabled fast boot-up in Win8, ie. enabling complete shutdown).
All I care is that now it is working for me, even though the root cause at least for the BIOS setup problem is still a mystery. I have longer Win8 boot up times now, so what? Watching those rotating dots a bit longer is kinda soothing. :)