Experiencing occasional blackouts

My monitor has been experiencing problems recently – it’ll go black, right in the middle of something. It doesn’t cut my internet connection; I can still hear the audio I’m streaming. I’ve had the computer for just over two years and I’ve updated to Yosemite, but I’m still having problems. I’ve even done a safe boot, to no avail. Is there anything else that can be done? Willie Holmes This sounds like the graphics card is overheating. The fact that your screen only blacks out after a period of use is a cause for optimism though. All Macs pull air in through vents at one end and blow it out at another end. This inevitably sucks dust in as well and this gradually builds up to form an insulating blanket. If you can get rid of the dust, you should be able to restore the normal operation of the graphics card. If you have a Mac Pro or a Mac mini, first of all, it’s worth double-checking that the monitor itself hasn’t failed, by testing it on another monitor or TV. If it still blacks out, you just need to open up the case and blow the worst of the dust away. Don’t use a vacuum cleaner – these can generate static charges that will destroy the motherboard. Good old fashioned lung power is best.

But my intuition tells me that you probably have an iMac. Since they have less space inside the case and nobody normally opens them up, they suffer more from dust build up than other Mac designs.

I’ve had three iMacs die over the years from overheating, each after three to five years of daily use. The procedure for opening the case depends on which model of iMac you have. On the Mid2011 model, the front glass is only held in place with magnets and you can pull it away using strong suction cups. The thinner Late 2012 model uses glue as well, so you’ll need to soften this with a hair dryer and prise it away with a credit card or guitar plectrum.

Be sure to back up all your data first and then have a look at the guides for your model at ifixit.com.