No, I know my IP address, I put it in aswell as the WPA and DNS but still it says unable to obtain IP address
You have not provided your router brand and model and as such this is as good as we can help you. Moreover, any changes that you've recently done to your network like, changes in router setting, new clients, etc.
Based on what you have stated above, you are doing manual setup. Make sure no other device is using the IP address you are manually assigning to the PS3. Make sure you are entering the right network information, subnet mask, router/gateway IP, the correct wifi password etc.