I installed 12.04 LTS 64 bits from a USB drive, but I can't seem to boot from the HDD. I have a single partition, with no other OSes. I need to plug in the USB drive for the PC to boot Ubuntu. Is my install OK?
I'm no expert but could it be that you installed the boot loader GRUB on your USB drive? Would explain your problem to me.
When you have booted succesfully, you can check your boot loader location from a Terminal while the USB drive is mounted:
You will get a output like that:
The * indicates the boot loader location. When it is listed somewhere on your OS HDD, I was wrong.
If I was right, I will post a solution when you commented to my answer. I don't want to talk you into doing the wrong commands and break you installation completely.
I had similar experience after latest install - GRUB install failed.
First of all check your BIOS boot order settings - is your disk enabled at all?
If that is OK following one of "How to fix GRUB2" guide should get it fixed. Try this one at WebUpd8.
If command line doesn't suit you, you can try Boot-Repair graphical tool.
means that your bootloader (GRUB) is installed on this USB disk, but not on your hard disk.
Solution is simply to install GRUB in the MBR of your hard disk. You can do it for example this way:
Or you can use the Boot-Repair graphical tool.