When using a PC with the HD in it and trying to install the Ubuntu from a USB to another USB. the installation does not recognize the USB, and wants to install on the HD. And you can guess, I have messed up my HD not paying attention to this. IS there anyway to proceed the way I am trying to do or I have to take the HD out of the PC so there won't be any accidents.
If I understand you correctly, it sounds like you may need to simply switch your boot order. It sounds like the computer's BIOS/UEFI stuff is telling the computer to boot from the HDD before it tests the USB drive.
When you start your computer, watch the corners of the screen for a line of text that says something like 'F12 for BIOS' or some variant thereof. Some usual keystrokes are "del", "F12", "F10" and "F2". This should take you to a screen that has some tabs. Once there, look around for something like "Boot Devices" and once you find that, "Boot Device Priority" or "Boot Order" should be close by. Move the USB Entry above the HDD entry and you should be able to boot from the USB without removing your USB.
== Also ==
In some instances (like my own motherboard that I had to flash update, a GA-970A-UD3 GigaByte board), booting from USB didn't work, so I needed to update my motherboards BIOS. Unlikely, but possible.