I want to use the live cd (Linux mint 9) to do a repair install on my system, but when I start, it says that it has detected another instance of linux and this must be removed before I can continue. I don't want to do this as I have a lot of data on this system and I don't want to lose it.
The error occurred when I did a dist-upgrade and installed new kernels.
Before I installed the kernels, a message came up saying the following packages are already installed but are no longer required. Use apt-get autoremove to remove them. I did this and now when I boot, I get as far as the five changing dots on the screen and it just stays there. I went into command line and ran apt-get mint-meta-main mint-meta-gnome, and at the end it came up with problem with /etc/utilities/desktop.
dpkg error 1.
Any ideas please.

I don't think you can do a 'repair install'.

You can use the Live Disk to repair your system manually, or even to get the important files and back up your system... but you can't install over the top of Mint without getting rid of the previous 'borked' install.

I have heard of people installing over the top, and just not selecting the 'format disk' option in the partition editor, but I'd consider this maneuver way too risky to try...

What I would do, is pop in the live disk, and use that live disk to retrieve your important files. You could burn em to DVD/CD, put em on a thumb drive, or even shrink down the original partition your system is on, and put all of the files on a dedicated partition...

Sorry about your luck, but unless you want to repair your system, which might not be overly difficult, depends on the problem, you're going to have to write over the last partition.

another solution might be to do the side by side install... giving you the option to dual boot into a working OS, and retrieve your files on the borked OS... that seems like too much work to me, I'd probably just toss em all on a thumb and be done with it.

If you reinstall, create a separate partition for /home
So you can reuse it when something goes wrong.
Also consider using a good backup strategy.

Was the original install Mint9?

Try this, use a livre cd (knoppix or Mint) and copy /boot directory of a system that's boot normally on yours /boot dir.
If you use grub, don't overwrite grub dir. Maybe you have problems with some hardware but you can boot and try to fix your installation.

I second albert1t0.

I would recommend Knoppix for this--this is exactly the type of task it is designed for. Heck, I know Windows guys who use Knoppix to fix Windows.

I would build on what albert1t0 said by suggesting that you also copy the contents of your home folder, at least the crucial files, to removable media. And do not forget crucial hidden files.

You can also use Knoppix to look at /etc/utilities/desktop and maybe diagnose and fix the problem by editing some text file without having to reinstall.

Aside: I remember encountering the "Repair" option in Windows NT, and 2k, and XP (I haven't messed with Vista or 7). Frankly, I never ran a Windows "Repair" that repaired anything; all it did was waste an hour or two. If I tried to run a "Repair," it always ended up "Reinstall."

Most of the mega-distros (Ubuntu, Fedora et al) and their derivatives like Mint are pretty arrogant when it comes to this. They only recognise themselves when they are the only (or "first") distro found on the hard-disk. Same generally applies to "boot an installed system on hard disk" type options.

I usually just do a full re-install and ignore the distro attempt to recover. As per @repo above, you might want to create a separate partition and copy /home over first. The re-install will handle things for your userids if you specify the home partition during the install. At least normal Ubuntu does ...