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

It will not show you drivers, but if you can post the exact model/year, then I can suggest methods for getting the correct driver list.

What is the exact GPU in your iMac?

In OS X System Report or Windows Device Manager -> Display Adapter will provide details.

1. From iMac (21.5-inch, Late 2015) - Technical Specification, the GPUs you may have are

Graphics

• 1.6GHz
  Intel HD Graphics 6000
• 2.8GHz
  Intel Iris Pro Graphics 6200

2. From iMac (Retina 4K, 21.5-inch, Late 2015) - Technical Specification , the GPU you have is

Graphics

Intel Iris Pro Graphics 6200

From Identify the model of your iMac - Apple Support, your iMac16,2 is the Retina 4K.

If I look in Bootcamp.XML for BC6 6.0.6237 which is meant for your Mac model, the INF files are

<InfInfo>

<Name>Apple USB Ethernet Adapter

<InfName>AppleUSBEthernet.inf</InfName>

<Name>Apple USB Ethernet Adapter

<InfName>AppleUSBEthernet.inf</InfName>

<Name>Apple Built-in Bluetooth

<InfName>AppleBT.inf</InfName>

<Name>Apple Built-in Bluetooth

<InfName>AppleBT64.inf</InfName>

<Name>Apple Broadcom Built-in Bluetooth

<InfName>AppleBTBC.inf</InfName>

<Name>FaceTime HD Camera

<InfName>AppleCamera64.inf</InfName>

<Name>Apple Display Driver

<InfName>aaplmonf.inf</InfName>

<Name>Apple Display Driver

<InfName>aaplmonf64.inf</InfName>

<Name>USB Keyboard HID Filter

<InfName>Keymagic64.inf</InfName>

<Name>Apple Multi-Touch

<InfName>AppleMTP64.inf</InfName>

<Name>Apple HID Filter

<InfName>AppleTPP64.inf</InfName>

<Name>Apple Null Driver

<InfName>AppleNull64.inf</InfName>

<Name>Apple ODD

<InfName>AppleODD.inf</InfName>

<Name>Apple ODD

<InfName>AppleODD64.inf</InfName>

<Name>IR Receiver Filter Driver

<InfName>IRFilter.inf</InfName>

<Name>IR Receiver Filter Driver

<InfName>IRFilter64.inf</InfName>

<Name>Apple SD Card Reader

<InfName>AppleSDR64.inf</InfName>

<Name>AppleSPIDevice Service

<InfName>AppleSPIDevice.inf</InfName>

<Name>AppleSPIKeyboard Service

<InfName>AppleSPIKeyboard.inf</InfName>

<Name>AppleSPITrackpad Service

<InfName>AppleSPITrackpad.inf</InfName>

<Name>Apple Wireless Mouse

<InfName>AppleWirelessMouse.inf</InfName>

<Name>Apple Wireless Trackpad

<InfName>AppleWTP.inf</InfName>

<Name>Apple Wireless Trackpad

<InfName>AppleWTP64.inf</InfName>

<Name>System Device

<InfName>NullSystemDevice64.inf</InfName>

<Name>Apple Solid State Drive Device

<InfName>AppleSSD.inf</InfName>

<Name>Fresco Logic xHCI (USB3) Device Driver

<InfName>FLxHCIc.inf</InfName>

<Name>Fresco Logic xHCI (USB3) Hub Device Driver

<InfName>FLxHCIh.inf</InfName>

<Name>Bluetooth Driver Management Service

<InfName>BtwSerialBus-dev.inf</InfName>

<Name>CS42xxUpperFilter

<InfName>cs4208_28.inf</InfName>

<Name>CS420xLowerFilter

<InfName>cs420x_46.inf</InfName>

<Name>CS42xxUpperFilter

<InfName>cs4208_27.inf</InfName>

<Name>AMD Audio Bus Lower Filter

<InfName>amdkmafd.inf</InfName>

<Name>Broadcom 802.11 SDIO Network Adapter Driver

<InfName>bcmwl6.inf</InfName>

<Name>Broadcom 802.11 SDIO Network Adapter Driver

<InfName>bcmwl63.inf</InfName>

<Name>Broadcom 802.11 Network Adapter Driver

<InfName>bcmwl6.inf</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver

<InfName>e1e6232.INF</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver K

<InfName>e1k6232.inf</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver Q

<InfName>e1q6232.inf</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver R

<InfName>e1r6232.inf</InfName>

<Name>Intel(R) Gigabit Network Connections Driver

<InfName>e1y6232.INF</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver

<InfName>e1e6232e.inf</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver K

<InfName>e1k62x64.inf</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver Q

<InfName>e1q62x64.inf</InfName>

<Name>Intel(R) PRO/1000 PCI Express Network Connection Driver R

<InfName>e1r62x64.inf</InfName>

<Name>Intel(R) Gigabit Network Connections Driver

<InfName>e1y62x64.inf</InfName>

<Name>Intel(R) Serial IO GPIO Driver

<InfName>iaLPSS_GPIO.inf</InfName>

<Name>Intel(R) Serial IO I2C Driver

<InfName>iaLPSS_I2C.inf</InfName>

<Name>Intel(R) Serial IO SPI Driver

<InfName>iaLPSS_SPI.inf</InfName>

<Name>Intel(R) Serial IO UART Driver

<InfName>iaLPSS_UART.inf</InfName>

<Name>Intel(R) Serial IO GPIO Driver

<InfName>iaLPSS_GPIO.inf</InfName>

<Name>Intel(R) Serial IO I2C Driver

<InfName>iaLPSS_I2C.inf</InfName>

<Name>Intel(R) Serial IO SPI Driver

<InfName>iaLPSS_SPI.inf</InfName>

<Name>Intel(R) Serial IO UART Driver v2

<InfName>iaLPSS_UART2.inf</InfName>

<Name>Broadcom Simple Communications Device

<InfName>B57Ports.inf</InfName>

<Name>Broadcom Simple Communications Device

<InfName>B57Ports.inf</InfName>

<Name>Broadcom NetXtreme Gigabit Ethernet - NDIS 6.0

<InfName>b57nd60x.inf</InfName>

<Name>Broadcom NetXtreme Gigabit Ethernet - NDIS 6.0

<InfName>b57nd60a.inf</InfName>

<Name>Intel(R) HD Graphics

<InfName>igdlh64.inf</InfName>

<Name>Intel(R) Display Audio"

<InfName>IntcDAud.inf</InfName>

<Name>Intel(R) HD Graphics

<InfName>igdlh64.inf</InfName>

<Name>NVIDIA nForce Ethernet Driver

<InfName>nvfd6x32.inf</InfName>

<Name>Service for NVIDIA High Definition Audio Driver

<InfName>nvhda.inf</InfName>

<Name>NVIDIA System Driver

<InfName>nvsmbus.inf</InfName>

<Name>NVIDIA System Driver

<InfName>smuc.inf</InfName>

<Name>NVIDIA nForce Ethernet Driver

<InfName>nvfd6x64.inf</InfName>

<Name>Service for NVIDIA High Definition Audio Driver

<InfName>nvhda.inf</InfName>

<Name>NVIDIA System Driver

<InfName>nfsmb64.inf</InfName>

<Name>NVIDIA System Driver

<InfName>smuc64.inf</InfName>

<Name>Service for NVIDIA High Definition Audio Driver

<InfName>nvhda.inf</InfName>

<Name>NVIDIA Stereoscopic 3D USB driver

<InfName>nvstusb.inf</InfName>

<Name>Broadcom Corporation System Driver

<InfName>bScsiSDx.inf</InfName>

<Name>Broadcom Corporation System Driver

<InfName>bScsiSDa.inf</InfName>

<Name>Intel(R) Display Audio"

<InfName>IntcDAud.inf</InfName>

<Name>Intel(R) Display Audio"

<InfName>IntcDAud.inf</InfName>

<Name>Intel(R) USB 3.0 Host Controller Switch Driver

<InfName>iusb3hcs.inf</InfName>

<Name>Intel(R) USB 3.0 Host Controller Switch Driver

<InfName>iusb3hcs.inf</InfName>

<Name>Intel(R) USB 3.0 Hub Driver

<InfName>iusb3hub.inf</InfName>

<Name>Intel(R) USB 3.0 eXtensible Host Controller Driver

<InfName>iusb3xhc.inf</InfName>

<Name>Intel(R) USB 3.0 Hub Driver

<InfName>iusb3hub.inf</InfName>

<Name>Intel(R) USB 3.0 eXtensible Host Controller Driver

<InfName>iusb3xhc.inf</InfName>

<Name>NVIDIA Display Driver

<InfName>nvao.inf</InfName>

<Name>NVIDIA Display Driver

<InfName>nvao.inf</InfName>

<Name>AMD Audio Bus Lower Filter

<InfName>amdkmafd.inf</InfName>

<Name>AMD Audio Bus Lower Filter

<InfName>amdkmafd.inf</InfName>

<Name>AMD PCI Root Bus Lower Filter

<InfName>amdkmpfd.inf</InfName>

<Name>AMD PCI Root Bus Lower Filter

<InfName>amdkmpfd.inf</InfName>

<Name> "Advanced Micro Devices, Inc." Display Driver

<InfName>C0295241.inf</InfName>

<Name> "Advanced Micro Devices, Inc." Display Driver

<InfName>CU295241.inf</InfName>

<Name>AMD Function Driver for HD Audio Service

<InfName>AtihdWB6.inf</InfName>

<Name>AMD Function Driver for HD Audio Service

<InfName>AtihdWT6.inf</InfName>

<Name>Intel(R) USB 3.0 Host Controller Switch Driver

<InfName>iusb3hcs.inf</InfName>

<Name>Intel(R) USB 3.0 Host Controller Switch Driver

<InfName>iusb3hcs.inf</InfName>

<Name>Intel(R) USB 3.0 Hub Driver

<InfName>iusb3hub.inf</InfName>

<Name>Intel(R) USB 3.0 eXtensible Host Controller Driver

<InfName>iusb3xhc.inf</InfName>

<Name>Intel(R) USB 3.0 Hub Driver

<InfName>iusb3hub.inf</InfName>

<Name>Intel(R) USB 3.0 eXtensible Host Controller Driver

<InfName>iusb3xhc.inf</InfName>

</InfInfo>

<FileInfo/>

</BuildInfo>

These are the two you need to install to correct the problem.

If you have the BC drivers USB you can run the Intel setup.exe. How much effort is it to reinstall Windows?

If you have activated W10 at least once, Microsoft now registers your hardware, so repeat installations are allowed.

1. Use only BCA to remove Windows.

2. Disconnect from the network physically when you see the first screen of the Windows installer where you choose the partitions to install Windows.

3. Do not connect to the network till Windows is fully installed, BC drivers are installed, an account has been created, and you have created a Windows System restore point. This restore point will avoid the nasty mess you are currently in.

4. Once you are this point. You can enable updates, but be aware that the problem you currently have will come back very quickly.

5. Till M$ can sort this out, I suggest disabling Automatic Updates and manually checking every week and only applying security updates. Do not apply any driver updates.

Can you check Windows 10 crashing, but not sure why. ? This may help ensure the WU is being disabled.