What is using up my hard drive

I've been running 7 since it was released and I have a 500gb hard drive.

When I click properties on my C drive it shows 129gb used.

I've checked every folder and cannot find any that appear to be too large or over 15gb. 

I don't have a lot of software installed and can't see why I'm using 129gb.

I ran a program called windirstat and it shows the C drive as using 45gb.

Is there a Win 7 program or command that I can use to find what is using 129gb?

 

Thanks

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