Raja - Sorry its taken me a few days to respond but I have been carrying out further testing to resolve the issue.
Note that the issue has been resolved...! but the process of elimination and resolution was somewhat lengthy - however I'll try and keep my reply brief.
The next few points will seem to have nothing to do with the UEFI locking up with profile selection but my memory failing when running Memtest led me to resolve the issue - So I am just posting this up for any others who may come across the same issue.
As mentioned in my opening post - I was having issues with the UEFI locking up when loading profiles. Another issue I had with this new build was that my memory would fail Memtest only 30 secs or so into the tests. Note that testing within Windows was 100% OK - It would simply fail when testing with Memtest in a DOS environment.
At first I had assumed that these two symptoms were unrelated - however it transpires that I was incorrect.
I had removed the memory and returned to my local store where they tested the memory overnight without issue. I then loaned some different memory to try in my setup which also proceeded to fail in the same way. At this point I had thought that the MB was faulty - Again wrong...!
My system runs a custom water-cooled loop which makes it a bit of a pain to remove and install the MB. However I had to remove the MB and I then proceeded to test on my bench with the Intel stock cooler. At this point I noticed that the memory was testing OK. So this confused me at this point in time.
To try an isolate further - I also swapped power supplies to no avail. I got to the point where I was running out of options. The only thing left was that when the MB was placed in the case, the only extra bit of hardware connected to the MB was my Aquaero 6XT controller. This connects to the MB via a simple USB header. When I was testing on the bench with the stock Intel fan cooler the Aquaero was not required and therefore disconnected from the MB.
To cut a long story short.... The Aquaero computer was plugged into USB port #14 - This is the one also utilised by the ROG Extension panel.
For whatever reason when the Aquaero was connected to this port - it would cause Memtest to generate false positives as well as causing the UEFI to lockup when recalling saved profiles...weird. In a Windows environment everything seemed to be A-OK.
Anyway - moving the Aquaero over to one of the other headers resolved both issues.
Obviously the shared ROG-EXT USB port is not quite the same as the other internal USB ports....!
Only wasted a few days on this ...:D
There may also be an error in the manual as on pg1-41 it refers to USB #13 on the ROG_EXT header but I found that USB #14 is the one that was working for me and the lower 4 pin port was not.
I have still been testing and playing with bios settings etc and I have now come across another variable which is causing the UEFI/BIOS to lockup - again whilst loading a profile.
This one should be easy to verify by anyone as I have narrowed it down to what is causing the lockup.
If you set the Boot\CSM menu as follows:
Launch CSM: Enabled Boot Device Control: UEFI and Legacy OPROM Boot from Network Devices: Legacy OPROM first Boot from Storage Devices: Legacy OPROM first Boot from PCI-E/PCI Expansion Devices: Legacy OPROM first
Now save this configuration into a profile and reboot etc.
Re-enter UEFI but now disable CSM ie: > Launch CSM: Disabled
Save this new config into a another free profile and reboot.
So now you should have two identical profiles saved with only the CSM mode being disabled in one and the other supporting legacy MBR boot etc.
Select and load the profile which has CSM enabled reboot and renter UEFI and confirm CSM support is enabled.
Now try and load the other profile which has CSM support set to disabled.
You should/will find that the UEFI locks up as soon as you hit enter to try and load that profile.
Raja@ASUS wrote: this seems like a highly unlikely scenario for many people.
Only stumbled on it myself as I generally have two profiles setup on my PC.
One which is my normal overclocked profile with the PC running on the edge so to speak.
The other is a standard [default setting] non overclocked profile which I always revert to when flashing MB bios or Video card Bios etc.
I have CSM disabled in my overclocked profile to speed up boot times somewhat but CSM is enabled in my 'default non-OC' profile so that I can boot off a non UEFI USB stick/CD as required - usually so I can perform some low level DOS work.
This is when the issue raised its head...:D
No big drama either way as now that I know what is actually causing the problem it is relatively easy to work around it.
Thanks for posting your issue with CSM UEFI lock ups. I just installed a new Z97-AR (bios v2012) and have run into exactly the same issue. My system locks when loading any profile with CSM "toggled". If I try to change CSM to disabled, Save and Exit, my system will NOT post. I am now troubleshooting but wanted to say thanks since your issue is very similar and most people don't reply with solutions and also to see if you had any ideas concerning a no post/blank screen when disabling CSM. By the way, Windows 10 Tech Preview runs fine after booting with CSM enabled using any variation of UEFI/Legacy options. I'm suspecting my ASUS GTX 750 TI video card?