For the next week use the canned air on the vents daily.
For the next month use it weekly then go back to your regular 1st of the month routine and how it clears up.
If not, have a tech replace heatsink compounds inside the laptop.
From some time i see these dots everywhere when i am using my gpu but when i disable it the problem is no more.
Some images i atached below.
Mention: i have a notebok acer 5755g with i3 and gt540m 2gb.
http://s16.postimg.org/df3khnyht/20150711_154109.jpg
http://s16.postimg.org/s4oem60rl/20150713_205502.jpg
http://s16.postimg.org/av7xnkaxt/20150713_230821.jpg
http://s16.postimg.org/iy63yvvj5/20150713_230834.jpg
http://s16.postimg.org/ve2tsmov5/20150713_235638.jpg
http://s16.postimg.org/ju2lec57l/20150714_015353.jpg

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