There is nothing special to find what was the date when you installed Windows on your computer or may be there is some case you want to find. However, if you want to find out original installation date of Windows operating system on a PC then here is a simple process to do that.
Run the cmd from Start menu
Type this command in Command Prompt, hit the Enter button and let it complete the processing for few seconds
Now, see it shows the original installation date and time of operating system