There are multiple instances when you would want to wipe your PC's memory clean and reset it to the factory defaults. Called "formatting," it is often the last-ditch effort to restore a PC to functionality. You will also have to format your PC if it gets crippled by viruses. Although these instructions are for the Compaq Presario, the steps are essentially the same for all Windows-based PCs. Be sure that you want to delete everything--this process is irreversible.
Back up any data that you want to keep by saving it to removable media, such as external hard drives, flash drives, DVD-R, etc. Unplug all peripheral devices, except for the keyboard and mouse.
Turn on the computer. As the computer is starting, repeatedly press F1 to initiate the recovery process. When the BIOS set-up screen appears, press the right arrow key to select "Boot". Press the down arrow key to select "Boot Device Priority" and press "Enter".
Press the down arrow key to select "CD-ROM" and press "+" to move it to the top of the list.
Open the CD-ROM tray, and insert the system recovery disk. Exit the BIOS set-up by pressing "F10". Be sure to select "Save Changes and Exit".
System recovery should initiate. If it does not, and the PC loads Windows, then you have either failed to set the CD-ROM at the top of the boot priority list or you exited the BIOS set-up without saving.
Press "R" to begin the recovery process. When prompted, select "Full System Recovery".
Restart the computer when the process has completed.