Why do programmers assume that "C:\" must exist under Windows ? When I reinstalled Windows on my PC I had an external card reader attached, and because the hard-disks are attached to the motherboard RAID controller, through the weirdities of drive letter assignment the Windows boot drive ended up on J.
Every so often I trip up because of this. The latest example was found when trying to install Garmin MapSource data, admittedly an older version. Despite successfully installing the updated MapSource application to J:\, that application could not install the map data directly from the CD - I had to use the original installer.
Fortunately, I discovered that inserting my USBdrive took over "C:\" and allowed the installation to continue, even though C:\ was *never accessed*.