I've had my 1st Gen MacBook for 1,5 years now and I've never had any problems with it. After it had been very slow for some minutes with only two apps open - iTunes and Safari, I restarted the MacBook. When after 15 minutes, it hadn't booted (it stopped at the grey screen), i put in the installation disc. It told me to choose a volume, but didn't show my hard disk as an option. I suppose there's something wrong with the harddisk. How do I fix it?