OK so found the solution, posting here for reference.

Turns out, for whatever reason, sticking a USB 3.0 drive in a USB3.0 slot causes the error, it wont read.  Completely counter-intuitively, if you stick it in a USB 2.0 drive, all works well. 

What is completely weirding me out though, on my other rig, exactly the same setup, the USB is in slot 3.0.. lol.

Answers on a postcard

OK so I've tested multiple USBs, and also rolled back not just the BIOS to a previous incarnation, but also to a prior version of SMOS.

It just seems that this B250 doesn't like SMOS, it happily recognises a regular usb with files on it, but as soon as I format it with SMOS, it fails to detect it.

Not sure what else to do at this point, other than try another OS.

You mean reinstall/reflash the OS on a new USB?

I'll try, was a brand new usb drive tho!

Title pretty much explains. This is my second rig, 1st runs SMOS on a B250 no problem, so decided to clone the same setup for our 2nd rig. However, for some reason, the mobo no longer recognises, and therefore won't boot from, the usb which is formatted to run SMOS.

Firmware is updated, v1001, cards all register, but if I go into BIOS with the SMOS drive attached, it won't even give me the option to boot from usb, let alone select it as a bootable drive.

If I try with another usb drive it picks it up fine.

Anyone know what's up? TIA you beautiful people!

Awesome thank you Brother 

No I didn't know about it til you said, I will try it if you think it will help.  Will that reset everything, back to default settings?  Unfortunately I am away from my rig right now and can't test it but thanks for the suggestion 

Hey all

I'm building a new rig and had the BIOS on the monitor, changed one setting, saved and restarted and now all I get is "No Signal" displayed on the monitor.  Everything appears to power on, CPU fan spins, ethernet port lights are on etc, but I just get no signal to the monitor.

I've tested different USB ports, different HDMI ports, etc. but I can't get the BIOS screen to show to reverse the setting.  The setting I changed was "enable CSM" - was looking for the option to boot from USB (to run SMOS).

Running latest firmware (1001), intel processor, ddr4 ram etc.

Anyone know what to do?  It's driving me nuts lol.

Cheers in advance  

oops sorry 

Hey everyone

1st post so apologies off the bat if I mess up

Am trying to build a 12 x 1080ti rig.  Have 8 cards running stable, issue is when we try to add more than that, system crashes.

Using:

PNY GeForce 1080ti
Asus B250 mobo
HP 1200W PSU (x3)
Corsair TX550M PSU
2 x 4gb RAM
Intel Pentium cpu (forget which)

Running SMOS, 50/300/200W.  HP PSUs running the GPUs and risers, Corsair PSU just for the mobo.

One thing I thought it might be which I haven't tested yet due to not having the right cable, is that the mobo has 3 x 24 pin PCIe slots (1 for each bank of 6 PCIe slots).  The Corsair only has 1 24pin so we only have one of the 3 connected.  Do you have to power each of the 3 if you have more than 6 gpus connected?  If so, would a 24 pin Y splitter work?

Have also seen some conflicting advice, asus saying maximum of 8 Nvidia cards, but YT vids aplenty showing 12 or more 1080tis on same mobo.

Anyone know what to do?

Thanks a million!