After trying to repair a boot problem I have now decided to try and install a fresh version ontop of the existing partision. But I get this error message of no root found. please see attachment

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You have to tell the installer what disk to use for root, /. If you do a normal install, the installer will usually do it all for you, but for a manual partition/install, you have to tell it what you want. Go back to the partition disks screen, select the disk and partition you want to use for /.

So are you saying for a maual instulation I need to patition it rather then try format it first?

I remember when installing win-xp; it gave you the option of pressing the L key and repairing a system. Do you know if there is an option for this please?

You are not installing Windows. Linux is not Windows. Very little is the same. On previous screens there were options to partition, format (or neither) disks, and to select where to mount /, /home, or whatever you might choose. You have to tell the installer where you want to install the filesystem. If you take the automated option and use the entire disk, it's easy. If you're trying to dual-boot, it's more complicated, and you really need to read and understand what you need to do. Or else you may destroy your Windows partition, assuming you have one, and I would bet the rent money you do.

Do not rely on the kindness (and knowledge) of random internet strangers. Put on your big boy pants and use Teh Google, and read multiple websites, and make sure you know what you're doing. You may be unhappy otherwise. I'm sorry, but I can't see your computer, or follow what you're doing step by step, and neither can anyone else. Linux assumes you know what you're doing, and will let you do anything, however ill-advised it might be.