I bought a refurbed HP desktop in June 2008. It's been fine up until about a week ago. Then I started hearing intermittent whirring sounds, but the computer continued to work properly. On Saturday, I had it on for about a half hour when it started making a continuous high-pitched whirring. Concerned, I shut it off. When I turned it back on, the whirring noise continued, even louder and the computer shut off before it booted up all the way. I took it to a local computer repair shop, but when the tech plugged it in, it booted up and didn't whine or shut down. Any ideas what could be going on? Thanks.