The only way to go back to stock (factory state) is flashing a backup, which is recommended before installing Cyanogenmod or any other custom rom. Other than that, if you're lucky, you can try and find the stock firmware for your P3113.
The issue of your P3113 not connecting to your PC via USB: Try powering off the tablet completely. Connect your tablet to your PC via USB. It should install the USB drivers. When it's done, disconnect your device, boot up the tablet completely. Connect the tablet to your PC again with the USB. If you don't see a change, try enabling USB debugging. I had the same issue with my P5113. This worked for me.