I purchased a memorex dvd-r with 4.7 gb. And when I tried to burn something, the computer tells me to put in another disc. I tried putting another different memerox dvd and it tells me the same thing. Is memorex a bad quality dvd-r? Should I buy a sony dvd-r? Which one should I get, the gold cover dvd-r or the blue cover dvd-r? thanks for your help.