Note: This method of converting MBR to GPT is destructive, ie you will loose all data on the physical hard drive this is being done to.
Step 1) Boot to command prompt as admin
In order to convert your MBR disk to GPT, you first need to boot into the command prompt as admin. Simply running it from within Windows will not work for this. You need to boot to it. Use the following guide to boot to the command prompt as admin:
Step 2) Once in command prompt, do the following:
The following will convert disk 1 to GPT disk.
1. In the command prompt, type diskpart and press enter.
2. Type list disk and press enter.
3. Type select disk 1 and press enter.(If you have just 1 physical HDD attached the select disk 0)
4. Type convert gpt and press enter.
5. Type exit and press enter.