IF it is really a burning smell, unplug it right now. After sitting for a few hours, either take it to get fixed or open it up and try to find the problem. Which you probably won't be able to DIY, anyway. Problems like this don't fix themselves and if left untended, almost always get worse (more expensive) to fix.
You may be able to clean out the dust.....that COULD be it, but it sounds like you've already begun the meltdown of a board.