Been running the P55-UD3R with an i5-750 no issues for a month or more at 4.2Ghz, lots of reboots and OCing.

Got a 660 today to mess with under cold water, but whenever I shut down, the only way to get the rig to boot up is if I reset the CMOS.

If I go into the BIOS upon first load and F10 out, it won't boot. Even though I didn't change or save anything.

Tried these BIOS:
F3n
F3m
F4 (latest)

Once I reset the CMOS and boot into Windows it runs just fine (like it did with the 750)

Any ideas? I see quite a few boot issue posts on the internet regarding Gigabyte P55 boards, some have solutions but are nothing related to what is happening for me.

Here be my 660 at stock (boring!) but can't do anything about that

http://valid.canardpc.com/show_oc.php?id=947733