I have just recently installed Ubuntu on an external hard drive, and can dual boot it on my laptop without problems. The problem came when I wanted to boot my laptop without having the external hard drive plugged in. I found that grub had taken over my boot program, and that I couldn't move it onto the laptop's internal hard drive. Any ideas as to how I can get the boot sector back, so that I don't have to plug in my other hard drive everytime I want to reboot?

The easy for me would be to create a small partition on your laptop hd say of 200 meg and install grub there to boot your distros and then when your external was not plugged it would still boot the laptop.

I am sorry for not being more detailed. I can give you a step by step but there are a lot of articles covering this. I will give you some links if you need or will try to help you with the steps. I will need more information if you are interested in doing it this way. You may want to Google a little.

Googling has yet to help me, as I have no clue what to look for. Admittedly, I am new to some of this stuff. What information do you need?

Welcome to LinuxQuestions.

I will guess that when you boot all you see is the grub boot prompt. Grub needs a file called menu.lst which is located in the /boot/grub directory. When your external hard drive is disconnected grub halts.

You can install grub to your external drive and set the BIOS to boot from USB first. Then restore the windows bootloader. To install grub to your USB drive type in a console window.

sudo grub

> root (hd1,0)

> setup (hd1)

> exit

Not knowing your setup I will assume that root is the 1st partition on the drive.

It is also possible to boot windows from the grub command line.
http://www.linuxjournal.com/node/4622/print

You can reinstall the windows bootloader using the install CD and boot the recovery mode then run the fixmbr command.

Something that might be easier for a while is download Super Grub and burn the cd as a ISO (image)and it will auto boot for you.

http://www.supergrubdisk.org/

basicly grub selects the root where it "lives" when you install the linux distro. if you go sudo grub and change the root (as it was explained by MichaelK) you can put grub into your external harddrive, leaving your normal drive untouched.
if after doing so you still have problems, you'll need a windows bootable cd (supposing you have windows on the laptop's hdd) and then you'll need to run the recovery console where you input fixmbr and fixboot
hope this helps.

Fedora Development