I have not had any problems with my new iMac for the past two months, but yesterday I was working in PowerPoint and the comp. just totally shut down...screen went black and hard drive turned off. I waited about a minute to turn it back on and it turned on fine with no problems. Luckily I have my PP set to save every five minutes, but it still makes me feel uneasy. There was no freezing or any indication that the computer was unstable before it shut down. Has anyone else experienced random shut downs?