As my blue and white G3 is fading fast, I have bought a secondhand iMac G5. The seller has removed the OS X (manually perhaps?) and sent me the two Install discs. These will not install without the Administrator's password (not even to allow me to change it). The seller sent me a string of his usual passwords, but none works, and he referred me to you. What should I do? (I live in the UK). Thank you.