I wasn't asked, but I'm gonna toss in my 2 cents worth. First and foremost, there are two partitions on that disk. The first, Partition 0, is labeled D and contains the original Windows installation. This first partition is normally the boot partition.
The second partition, Partition 1, contains your current Windows installation.
What really concerns me is this: the drive capacity is 640,000,000,000 bytes or 596 GB. You are using 326 GB in the two partitions, leaving 270GB unaccounted for. I can think of many reasons for this, with few of them good.
Louis is correct. If you have the media and a valid product key, I would save off any critical data files, delete ALL partitions, , making sure the entire 596GB is available, and do a clean install of Windows. Your only real concern is to get the latest device drivers from the maker, or the motherboard mfr. The disk strip and reformat functions can be performed from the windows 7 installation program on the DVD.
On re-reading the Speccy report, it is possible that you have not allocated the missing 270GB. Right-click on My Computer, select Manage, and select "Disk Management". When the screen comes up, you should see two partitions displayed with a third area that says "Unallocated". If that's the case then the questions are answered. I would still suggest deleting all partitions with the Windows installer and doing a clean install of Windows.
Which brings up another question. Is this a commercial computer, ie was it made by someone like Dell or Acer, or did you build it? In other words, who made it and what is the model number? DO you have the installation media and a valid product key for Windows 7? You seemed to indicate that you did in your original posting.
There are many good tutorials on how to install Windows 7 and how to format and repartition the disk. If the disk is more than 4 years old, I would replace it.
Finally, you have a 64-bit OS loaded and running, but only have 2GB of memory installed. I would install another 3 sticks of memory (of exactly the same type and part number) to bring it up to 8GB. 4GB (one more stick) is the very least I would use with a 64-bit OS. Otherwise the machine spends far too much time swapping stuff into and out of the page file, which makes the machine very slow.