Hello, I just got a username on this website because of this thread. It is the most relevant to the problem I am having right now, although not completely helpful to my knowledge. Here is my problem:

I just installed Ubuntu Linux onto an external hard drive. I restarted the computer, and GRUB was able to bring me into my newly installed Linux just fine. No problems. A while later, I needed to use one of my windows programs so I restarted and went into Windows XP Home. Later I wanted to go back into Linux, but my PC wouldn't restart. This a problem I have had for a while with Windows, where the restart doesn't work frequently. Given no other option, I had to press the power button to turn off the computer and turn it back on.

I got the GRUB error 21 message this time around. I turned the computer off and on again, and went into the BIOS to check if my hard drive was being detected. It is reading my Primary Master just fine (Windows Drive) but the Secondary Master (Linux Drive) seems to be undetected.

I suspect that the BIOS stopped reading the secondary (an external drive) when I had to manually turn off the computer. I was wondering if there was any way I could get the BIOS to detect my external again. If there is any more info I should provide, I'll do what I can. Hopefully the solution is right under my nose and simple.

I really have no idea what to do at this point. I guess I made the mistake of trying to install linux on my laptop thinking I was more knowledgeable than I truly am. I have an HP compaq nw8440 with a single 100gb hdd. It is a college laptop so XP was pre-installed and has to remain on there. I tried creating a partition on an external and installing ubu 8.04 on the partition so as to keep it off of my internal HDD (in an attempt to avoid problems )

So here is the info I have for anyone who would be willing to help. The installation completed successfully, but could not change boot priority to the linux installation. I went into the live cd and ran GParted to erase the partition and restore my external to previous state. Tried booting back into XP and got the Grub error 21. Other complications: I don't have a bootable XP cd since it was pre-installed on my laptop and I don't have USB floppy drive.

I will checking back religiously until I can get this problem resolved. I wish I could give you more info, but don't know what or how to get it - just let me know of anything else that would be of help and I can try and post it.

Thanks to all!

My problem was a corrupted or missing MBR, which must have occurred when I was trying to put linux on my system.

I checked an Ubuntu forum and saw a suggestion for Super Grub Disk. I burnt the image to a disk and booted up my laptop, selected the windows and put me right past the error I was having into windows. I just did this so I do not know if it provided me with a new mbr, but it at least successfully got me back into Windows so I can try and fix it from there.

Hello all, just today I reassembled my computer after giving it a good cleaning and reinstalled two of the three drives back in. I have one 80Gb SATA drive with Ubuntu V.7.10 and one 80Gb normal ATA drive that has Win 2000, the third drive is a 15Gb backup drive that used to have Win 2000 but got removed.

After leaving the 15Gb drive out I got Loading GRUB stage 1.5, please wait then GRUB error 21. I put the drive back in the computer and everything boots just fine.

Could someone help understand why it Linux needs this drive in order to boot even though there is nothing on it other than backed up documents?

Oh yes, I forgot to mention the fact that I want to remove the third drive because I no longer need it, so I would like to know what I would need to do to get my system working with out it if possible.