Nop... both are not yet activated...
Intel 180 and Vertex are both GPT disk, as seen from Diskpart..
I finally got the dual boot working with UEFI (I've even fall back to test the same thing in MBR)... and find that I've committed at least a double fault during the process:
1. I installed the INTEL rapid storage manager software (come with the Asus driver
disk) on the Intel 520 SSD..this will result in the hardware marker of the disk changed to SCSI...making the disk sometime not assessible for reading.. I skipped installing this software later on, which changed the HW marker to IDE
2. The boot sequence in the BIOS should always start with a DVD drive, and not the Window Boot manager.. I don't know the reason why... If I choose window boot manager as the first to boot, then only the 1st drive installed can work, and the 2nd drive install will always have the error "bootosmissing"..
BTW thanks for all suggestions which did help me to learn and come up with the final solution..