I don't get it.
What drives do you have at C: D: and E:?
If nothing, then you should be able to install a drive, or possibly create a
partition which can then be called C:, and onto which you can install the
problem program (which I assume is very old).
If you have drives labelled C: D: and E:, you may be able to re-letter them
using the Control Panel|Administrative Tools|Computer Management. In the
Disk Management element of Storage you will see any currently installed
drives, and be able to select new letters for them. Finally, you should be
able to map either a partition or a drive to C: so that you can install the
program.
Do NOT change the drive letter allocation of the drive/partition which
Windows is contained in, or you will kill the system.
HTH
Dave