(SOLVED)Full install to USB failed in desktop

I have tried to make a full install of Zorin 8 Core to a USB drive for my desktop, ASUS AMD Athlon 64 bit dual prosessor with NVIDIA Geforce 8500 + graphics card. All seems to install ok. but when I am booting it says "Error loading operating system". I have tried several times using a Kingston Data Travell 2.0/3.0 16 Gigs Drive. When I try that installation to my HP 530 laptop it says" Non system disk or disk error, replace and strike any key when ready". That is only info I can get out of that Zorin 8 Core on the USB.

All USB live installations works ok. with all os.es and both computers, and also the Zorin 8 Core full installation to USB drive with my HP 530 laptop.

There is something with Zorin 8 that don't fit with my desktop and USB full installation. I have not found any further solutions to make Zorin 8 Core to start to work as full install in USB. Any suggestions?

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I tried later on to install also from the DVD the os. but no diffrence, same error message came immediately after hitting "Enter"-

I found out that the boot loader was installed into the partition in the USB. It should be defined to be in the USB "Device". Now it works.

Other findings here:
- Full install USB is not portable like USB live due to HW configuration
- A high speed USB preferably USB 3.0 should be used also in a 2.0 port to get speed enough to executing
- Full install takes 4-5 times more space from a USB than live installation so a 16 Gb drive is minimum for Zorin 8 Core