Indeed, you must do a clean install of an OS. You can't use the current implementation.
However, you should be able to boot from a Linux Live disk to copy all your stuff to an external hard disk. Better do it twice to 2 different disks or copy the contents of the to anothre PC. If you only have one copy and you erase the original by installing the new OS, you don't have a backup any more! And with external hard disks being unreliable, that's a risk you don't want to take.
The idea of a new hard will surely work also, and is safer.
I recently installed new parts into my PC (mobo, gpu, cpu and ram) and when booting up i get the BSOD. I think my OS (XP) might not be recognizing my mobo (Dh77eb) without the drivers and i cant install them without properly booting. I thought about taking my HDDs out (C and D) and installing them into another comp to back up and my data so i can install w7 on my new PC but i dont have another computer to do this with. So instead I thought about unplugging my C and D drive and installing a 3rd HDD primarily for w7, after installing w7 I will replug my C and D drives back in. I will make it boot from my 3rd HDD. Will this work?