I have a former internal hard drive, which I now use as external USB drive. I tried to boot from it, but it doesn't work (2 PCs tried, on my: blank screen + blinking cursor). This - I think - is normal, because to make a USB device bootable it must be prepared before the installation / during formating.

Since I don't understand, if the situation of other threads here fit on mine, please tell me:

Is it possible to boot the system, which is already on the external drive (and which has worked, when it was an internal drive).

My ideas were:

• use this device in a virtual machine as already installed system or try to boot from it (which doesn't work, since it's not prepared).
• change grub on the system, where I attach the external HDD

Edit: I have used gparted to set the partition as active / bootable. Buuuut: it is a logical partition and not the first on the HDD. When I now try to boot from the computer gets into a reset loop: right after the BIOS messages my computer restarts instead of booting.

Thanks!