Windows 7 installer sets its own path as C:\ - cannot install to C:\

My Windows 7 installation is many years old, and gone through many hardware changes, software installations and uninstallations, and Windows itself has been getting progressively slower, buggier, and prone to odd crashes and hang ups. I decided to try repairing the installation with my original install disc, but found that my DVD drive is no longer functional. Having used the official ISO from Microsoft to create a bootable USB for my netbook worked swimmingly. For my desktop, not so much.

When booting from USB on my desktop, the Windows 7 installer mounts itself as drive C while detecting my existing Windows installation as being drive D when it is actually and most certainly C. I've tried forcing drive paths from within Windows, changing boot order, switching USB ports, all manner of UEFI options pertaining to USB... and it always sets the installer as C, unable to set the Windows install path to C because C is in use by the installer.

I'm a bit too paranoid to try repairing Windows for fear of it totally screwing everything up with the forced drive path change, and using a drive path other than C for a clean install is, at best, undesirable. Would also prefer not to spend money on a DVD drive that I will in all likelihood use exactly once.

Motherboard (which I'd wager is the culprit) is an embarrassingly flashy ASRock P67 Professional.

Toshiko said:

When booting from USB on my desktop,

That statement contradicts itself.

You don't boot from USB on the desktop.

If you are trying to do a clean install, you shutdown or restart and boot from the USB.

It's not contradictory, you misunderstood what I meant by 'desktop'. I meant 'desktop' as in 'not a laptop or notebook or tablet, but a full tower with a separate monitor'.

Maybe I did then, what did you mean by mounting?

That doesn't sound like it was booted to me, that sounds like an attempt at a repair or upgrade install especially since you say it was given a letter.

Okay. When you put the Windows 7 installation DVD in your DVD drive and reboot your computer, assuming the DVD drive has boot priority, it will boot up the Windows 7 installer. The installer will be ostensibly be mounted to a non-C drive path - D, or E, for example.

In my case, I cannot use my original Windows 7 installer because my DVD drive is kaput. I had to re-use a bootable USB image that I previously made for my netbook. On my netbook, the USB image mounts itself as D (which is the expected and sane behavior). On my [full tower desktop PC], the USB image mounts itself as C, and the installer claims it has found an existing Windows installation on drive D rather than its actual installation path of C:\Windows.

Interesting. I don't get any lettered drive path when I boot an installer. Maybe someone else has seen this.

What you are saying does not coincide with what should be seen when booting an installer, so there is no obvious reason we can see yet.

Can you post one of these,

Disk Management - Post a Screen Capture Image