Formating

You can do format while rebooting your pc and opening it in safemode command prompt that arrives by pressing F5 or F8.
First you format the drives in which your OS is not present.
Then format your primary hard drive on which OS is installed.
In command prompt write
C:/>formact C:\

OK a format will delete all programs. But if your data is confidential then you need a Hard eraser program to erase your harddisk completely before selling it. So use the program:
Darik's Boot and Nuke 1.0.7:
http://dban.sourceforge.net/
Download the ISO file "dban-1.0.7_i386.iso". Burn the image on a CD, restart the PC with that Bootable CD. This will start in a Linux Like interface follow the instruction and erase the drive you want with relevant erasing option.
Erasng will take time, so have patience.
After erasing it is safe to sell the PC, and now nobody can recover your data with any Data Recovery software.

bcdalai
http://bcdalai.blogspot.com/

BUT people who uses some kind of software can get all your private information off of there! so id recommend to get some Computer Wipe software

First of all you need to take backup of necessary files of your pc if you want. Second if you want to format your pc do delete all your data on other drive(like D:, E: etc in which operating system is not installed) without formating your drive. It is somewhat time consuming but it will not harm your harddisk life. Try to delete and remove all the folders you can from your logical drive(like C: on which OS is installed). I think at last may be 35 MB to 100 MB space will be conquered by the files which could not be removed. Then restart your pc and enter the cd of OS u want to install. Follow the instructions and and option will come to format your current hard drive. Do it your disk will be formated.

You can format the entire drive, however you will loose all stored information and all windows aswell as all your drivers will need to be reinstalled in order for the computer to be able to boot. How to format: When your computer is booting press F8 repeatedly until a black screen with a menu comes up, choose command prompt only or safe mode with command promt. The screen wil change and you wil have another black screen. At this screen type "format c:\" and follow the prompts.

Hope this helps