For models with pre-installed USB card reader such as the ST61G4, SN85G4 and RefleXion, etc, this could sometimes result in the card reader occupying the "C:" drive letter (as well as D, E and F). Since the card reader is pre-installed, it has automatically been allocated the first 4 drive letters (starting from C:). Try the below solutions to install your operating system on C: drive and avoid such issues: