-Make sure you have drivers for all of the hardware components.
-Make sure you have a backup of all your important documents
-Modify the BIOS configuration if needed to set the CDROM as the first device in the boot sequence.
-When the machine reboots make sure the OS installer disc is in the CDROM drive
-Follow the installer instructions to format the partition and perform a clean install of the OS
-Install a good antivirus program, and download the necessary virus definitions updates
-Restore your documents from the backup
-After installing the OS, change the boot sequence in the BIOS back to its previous value.
It is really a good idea to reformat a hard disk drive which is infected with various malicious software programs. If you are using Windows Operating System, you can use its genuine installation CD to reformat and install a fresh copy of the Operating System.
Reformatting your computer system also includes reinstalling the operating system. It is somewhat complicated to perform, so you really need to ask for a computer system to perform the reformatting and reinstalling of the operating system for you. Additionally, it is also hard to explain in writing.