CPU overheating, Fan ignores it.

I cleaned my cpu heatsink with pressurised air (which I have done many times before) without removing it from the motherboard. getting rid og all the dust so my computer wouldn't sound like a harrier all the time. I restart the computer and everything goes as normal, except it begins overheating when I enter a game. it goes from 50C to 100C in roughly 10 seconds.

Naturally I assume that I have destroyed my coolerfan in some strange way, however it is on a steady 2100 rpm as it usually is. When idling my the cpu is on roughly 50C, which is pretty normal. However when I enter a game or start rendering a movie, all software, bios etc register my temperatures going up and are hitting the 100C, however the fan continues on steady 2100rpm.

Normally there would have been a noticable speed increase of the fan, I don't know the number, but I can hear the sound of it when enter a game or start rendering. Now nothing happens, a low steady hum, my computer overheats fast and shuts down.

I checked pretty much everything, all wires are intact, nothing changed anyway with the hardware. Everything seems like before. I Entered the bios and disabled SmartFan, which should increase the fans speed to maximum at all times, however low steady hum and 2100 rpms.

I am no computer guru, however I am not completely lost and this just doesn't seem right to me. It is roughly a year old and I hope some air shouldn't have wrecked it already.

Guess some of you need speccs:
- Gigabyte Motherboard ex58 ud8p
- Core i7 930

Any good tips are more than welcome.
Thanks for any answers.