I just bought a MBA (1.3GHz) that came with Mountain Lion. I immediately upgraded to Mavericks and since then everything was horrible. Internet barely functions, and only does so periodically. It often takes minutes to load a text webpage. My chromebook and phone are meanwhile loading the same pages immediately from the same wifi. The wifi shows it is connected, but obviously the data is not transferring. So I attempted to downgrade back by going to Internet Recovery, erasing the hard drives (but the 0x hard drive would not allow me to erase it), and then reinstalling the OS. I had read that Internet Recovery would put the original OS back on, but it only offered to install Mavericks. So it took an entire night of downloading to reinstall the same OS I wished to get rid of. Despite this fresh install, the OS worked decently for about half an hour, and is now refusing to reliably load web pages again. So I am back to using other computers which still work fine. I attempted the trick of quitting wifi, deleting the network, and re-adding it, but no help. So how can I reinstall Mountain Lion without having any discs? I don't care about saving any data--I have nothing on the machine. If I can't fix this in one day I will send it in as a warranty replacement with disgust.