Won't boot

Well I've screwed this up.

PC is an i5 2500k, Asus P8Z67 V Pro, 3xSamsung SSD's.

Running flawlessly for years.

Earlier on I accidently picked the wrong setting for some memory and it wouldn't post. No big deal, reset CMOS, POST no problems.

Only since then it has refused to boot into Windows - I get 'The Boot Selection Failed because a required device was inaccessible'.

All my HDD's show up in the BIOS, but it won't boot.

It has to be a setting because all that changed was the CMOS reset but I've tried absolutely everything and am getting nowhere. I've had the HDD controller on RAID, AHCI, IDE, all to no avail.

I even get the same message when trying to boot from CD ROM.

Any ideas!?!

And now it works fine.

No idea why it didn't work. Most strange.