No Boot Device Found. Press Any Key to Reboot the Machine.

Hi..

At first I wanted my dell inspiron 3458 have dual boot with windows 7 64bit and ubuntu 14:04. Previous already installed windows, then I create a new partition in windows around 100GB for ubuntu. When the installation process ubuntu via USB, windows installed not illegible, then selecting options partitions "Something Else" also not illegible. 465GB's of HDD readable as unlocated space although have installed windows, that meaning the HDD is considered vacant by ubuntu. I try browsing to google, i follow some tutorials then found GPT HDD status is damage, while normal MBR. GPT I delete. Only drive C partition that can be read, another still unlocated. By the way, after convert the HDD GPT into MBR dynamic type, and then I turn it into a basic MBR simultaneously convert into basic GPT through AOMEI Partition Assistant. Finally all my partitions read and I managed to install ubuntu 14:04 in the drive that I want to. But I found a new obstacle, when boot process I found "No Boot Device Found Press Any Key to Reboot the Machine", this position booting as legacy. When attempting to boot with UEFI managed to get into windows or ubuntu. What happen with my legacy boot?
 
Can anyone help and give advice? Really needs help.