Similar problem here. My DQ45CB has been running as ESXi 4.1 server fine for 2 years, booting from an USB stick. I created a new ESXi 5.0 stick (partitioned with GPT). When booting, I only see a flashing cursor. Is this mobo capable of booting from GPT partitioned drives?
Update: Found a workaround: Press F10 during boot and select the USB stick. The boot then goes fine and ESXi 5.0 starts happy. if you let the machine auto-boot, it won't boot from the same USB stick. So it seems there is a problem in the BIOS when booting from GPT partitioned USB sticks. I use bios 133 (latest). Tried with and without UEFI boot, no change.
So Intel, can you please fix this in a new bios version?