As mentioned above, 30 C isn't too hot, and the fan switching into high gear is normal.
If you have a non-contact thermometer (IR) handy, you might take a reading on the heatsink of your video card just to see what temp it's at.
And of course, you can always install one of those slot-mounted auxiliary cooling fans, if you have a free slot. They're about $10 USD.
Sudenly they all vanished and only the desktop remained. It did this about six times as I sat and watched, then I switched off and left it for a few minutes.
To me, this sounds like something auto-updating in such a way that explorer.exe (not IE, but Win explorer) had to restart a few times. Usually something like this is handled during start-up as explorer launches, and the most you'll perceive is a "slow" start.
Have you recently installed any new software or made hardware changes?