Operating system acts as an interpreter between computer application and hardware. It works as an user interface.
You need to re-install another system, latest anti-virus software and an O.S with latest patches. Before you start your system, connect the infected HDD as a secondary drive then scan and clean the infected hard drive. Once done, you can copy the files into the system.
The maximum number of the logical drive that can fit on a physical disk is 24, while the extended partition can only have 23 logical drives.