Q: I bought windows on my mac and after using it for 20 days or so it has been working great but now it keeps restarting every 30 minutes of use and says diagnosing your PC then it says to restore the PC.Then it starts up fine but then the process restarts

1. What year/model is your Mac?

2. Are Windows Automatic Updates enabled?

If it is a 2015 model and you have W10 installed, there are very nasty issues as Windows Automatic Update pushes driver updates which break W10. Most common is the Intel GPU driver.

You can either boot in Windows Safe mode and remove the driver and re-install the one that Apple BC driver package provides, or re-install Windows, but disable Automatic Updates. 

Since your W10 installation does boot and stay up about 30 minutes, use Shift+Restart.

Please also see http://windows.microsoft.com/en-us/windows-10/start-your-pc-in-safe-mode .

You will need to remove the bad driver and replace it with the bC driver using PnPutil.exe . Please see https://technet.microsoft.com/en-us/library/ff800798.aspx .

Does it give you an option to boot in Safe Mode? For example - http://www.howtogeek.com/164876/how-to-use-safe-mode-to-fix-your-windows-pc-and- when-you-should/ .

Use pnputil -e to list the available drivers. Once you have a list, find the INF name from the Intel Iris driver. Use pnputil -d to remove the INF, which should also cleanup the Driver store and remove files associated with the specific driver.

If you can read the back of the iMac for serial number, please enter it in https://checkcoverage.apple.com/ and post the exact model. Please do not post your serial number, then we can find out which exact driver to look for?