So, you want to find out when was the last time you installed 
Windows on your machine? Since you’re reading this post, the answer to 
this question is probably yes. I’m not sure about you, but many simply 
feel that re-installing Windows at regular intervals – after a year, 
let’s say – keeps the system in optimal state. I wouldn’t argue with 
that theory, but in such a case, having a reference date of your last 
Windows installation does make sense. Or you might want to know about 
the date and time of your Windows installation just out of curiosity. 
Fortunately, then there are several different ways available to do that,
 which I will explain step by step, right after the break.
Windows Explorer Method
The first method comprises of taking help from Windows Explorer, and 
it’s surely the easiest (though not necessarily the most accurate) way 
of finding out the installation date and time. To do that, simply open 
the partition where the operating system is installed (usually drive C:)
 and right-click the ‘Windows’ folder followed by clicking ‘Properties’.
Under the Properties sheet of the Windows directory, you will be able
 to see it’s Created date and time. This date and time should be the 
same as when Windows was installed to your computer.

 
Earlier, I mentioned that this method may not be very accurate, and 
the reason for this is because since Windows Vista, many computers come 
with image-based installation media for Windows installation, which 
doesn’t exactly ‘install’ a new copy of Windows to the machine, but 
instead just replicates the image on the CD or DVD to the computer’s 
storage. As the date of actual creation of the Windows folder on the 
image-based installation media is not the same as the date and time at 
which you last used that media to reinstall Windows on your computer, 
the date will not be accurate. To cope with this issue, you can 
alternatively check the creation date of your ‘Users’ folder because 
this folder is created during Windows installation. Do note that this 
will give the accurate result only for the account that was created 
during or immediately after the installation.
SystemInfo Command Method
Another way of finding the correct Windows installation date and time is via the systeminfo command. Just open Command Prompt from your Start Screen or Start Menu.
Next, type the following command in the Command Prompt window, and press the Enter key:
systeminfo | find /i "date"
 
The tool will scan the information for youand show you your Windows installation date, as shown below.
WMIC Command Method
The third method is to use the Windows Management Instrumentation 
Command-line (WMIC). This method is also quite easy and displays 
accurate result.
First off, open Command Prompt as Administrator and run the following command. You can also refer to the screenshot below:
From the above screenshot, you can see that it displays a number. 
This number contains year, month,, date, hour, minutes and seconds of 
the installation date and time. According to the above screenshot, the 
number translates to 2012-11-05, 10:52:26
Registry Editor Method
The Registry Editor is another way of finding installation time and 
date on your system. This method is a bit more complex than the ones 
explained earlier, and require doing some manual calculation. 
Nevertheless, here’s how to do it.
Open Registry Editor via the Run dialog window or Start Screen.
Now go to the following registry location:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion
In the right pane that displays DWORD values, there will be an 
InstallDate DWORD. It carries the total number of seconds since 1st 
January, 1970 till the installation time, enclosed in brackets.
There can be a lot of ways you can use this number to calculate the 
accurate time. One way is to divide this number by 60, 60 and 24 to get 
the number of days between 1970 and the installation time, and then 
convert them to years by dividing with 365.25 (to account for leap 
years). There can be other ways too, including online converters that 
can calculate this duration for you automatically to show you the 
correct date and time.
This concludes our tutorial. If you have any additional thoughts or 
some other tips for finding the installation date and time, drop a line 
in the comments section below.
EnjOy..:)
Bugs Of Techn0l0gy