Home Forums Hardware Mac Desktops & Notebooks temporary screen & fan incident

OS 10.6.8 late 2009 imac. Yesterday and twice this morning, after booting up, the desktop screen went black for a few seconds and then the desktop became normal. I have just rebooted and it never reoccurred. Is this an indication of something I should know about? Secondly, for the first time I could hear the fan blowing upon boot-up so I rebooted and again the fan was very audible but after about 2 minutes, it was inaudible as usual. I realize the fan is is for cooling purposes but it must run at a very slow speed for me not to know it is actually running. Am I reading too much into this? jaybass