Instructions
Turn on your computer and see if it can access the Internet. If it can, skip to Step 3. If it can't, proceed to Step 2.
Unplug your modem and router and leave them off for at least 20 minutes before you plug them back in. Usually a DNS error refers to the connection, so once your modem and router come back online, see if you can access the Internet. If you can't access the Internet on your computer, it is not a problem with your PS3, it is a problem with your Internet connection. Call your Internet-service provider to fix the problem.
Unplug your PS3 from the Internet source and leave all cords unplugged for at least 20 minutes. Plug everything back in again. If it still will not access the Internet, click on “menu” and then “Internet Set up.” Set up your Internet connection again from scratch. If the Internet still will not come up, you might have a problem with the hardware on your PS3. Take it to a professional.