Before you discard your old computer, you need to wipe out all private information in it. Deleting is never enough. Some hacker using a data recovery software can access any data store in it.
Formatting your PC is not enough. This is because formatting does not real delete data from the hard drive.
You should carry out the following procedure:
Clear you cache to ensure your credit card numbers are not stored there.There are other sensitive information that will expose your identity such as email ID passwords, your names and social security number. These should also be wiped from the computer.
Start wiping data by saving it somewhere else. Then download a data wiping software. This software is free of charge.
Reboot with Dban.
Now your PC is ready to discard. Remember, if you are donating the PC it is a good idea to install some OS so that the new user can reboot the PC.