Two months ago my Monitor started producing black smoke, I immediately unplugged it and carried it into the garden.
The PC had only been on a half hour, the Monitor was completely clear none of the vents were covered, I bought the PC as new two years previously from a well known company.
Of course the Monitor was a write off, and a word or two of advice, don`t inhale too much of the bloody awful stinking smoke, so my friends beware in all mass produced items there is a hidden danger.