The biggest misconception with the casual tech folk is Mac's are impenetrable to hardware failures, for the most part the percentage of Macs crapping out on you are small,but when you have an issue on a large scale it becomes a serious issue that needs attention, especially when you have a rash of complaints coming from consumers. Which in turn is causing Apple to counteract this issues by instituting a Repair Extension Program.
The issues you ask? Its Apple current high-end 2013 Mac Pros equipped with AMD FirePro GPU which seems to be having drastic issues that includes a variety of symptoms, such as distorted video or no video at all, random system freezes, system restarts and shutdowns, and overall instability. In some cases, the problematic Mac Pro fails to even boot up into Mac OS X.
This issues is limited to the Mac Pro system that has installed the AMD FirePro D500 graphic cards and built to order Mac Pros that's equipped with FirePro D700 GPU's. Base model Mac Pro's equipped with the FirePro D300 isn't part of Apple's repair program.
Its not really known how many Mac Pro computers are affected by the defective GPU. According Apple support forums there is a thread that's dedicated to graphics issues that's taking place on the late 2013 Mac Pro models which oddly enough started in February of last year.
Thanks to the folks at MacRumors they were able to obtain a memo which entail Apple investigating of the problem at hand that led them to conclude that the GPU indeed is the main culprit of this problematic issue.
According to the memo, Apple has arrange for an authorized service provider to fix any eligible systems free of charge up until May 30, 2018. The expected turnaround time is 3-5 days.