I have a 5 year old iMac that has started to behave strangely. First Microsoft Office, which had been running just fine for years, now won't open (an error required it to close). When I installed OpenOffice.org, that also showed the same message when I fired it up. Other apps are closing suddenly at a rate much higher than previously. I have already applied advice I gleaned from the web, and forums. Problem persists. I figure that I might as well do my very first rebuild, rather than spending ages trying to figure out the problem. With the PC, it was an annual event, so I got used to it, but I've never had the need to rebuild a Mac. Are there any reliable web pages that tell how to wipe the hard drive and start again?