I'm sorry you may have lost some things you may regret. Whilst I have no idea at all how you ended up where you are now, I have some suggestions for your further checking. I also want to mention some things you can do to hopefully avert such problems in future.
Unfortunately, I have no idea if you are an 'experienced' windows user or not, so I must start by assuming you can follow me. If not, we can go a bit more slowly.
First off, is the data you mention deleted, lost or just hidden? Double-click recycle bin. Anything you recognise in there? This answers the simpler type of 'deleted ?' question. But if the deletion was malicious, it wont have been so stupid as to leave the deleted files in recycle bin anyway.
Next we can open administrative tools in control panel, and open properties of your C: drive. Select Tools and click 'check now'. (you are going to run chkdsk here). I recommend that at least to start with, you only check the drive, and do not allow any changes. In other words, untick both check disk options. After the check is complete, does it report any errors or not? We now know the 'lost ?' answer.
Next open windows explorer and select a folder where you know something should be but is no longer there. It is no use opening libraries, as the apparent files in there are actually just links to the real locations of the files. You can right-click a library folder, select properties and it will show you where the actual files are, which will typically be like 'My Music' is really C:\users\<your username> Open that actual folder location and see if there are any files dimmed out and therefore inaccessible.
If your basic problem is that the infamous Vista/Win 7 libraries feature is corrupt, see here
http://www.sevenforums.com/tutorials/114791-windows-media-player-rebuild-corrupted-libraries.html
Finally, if you get nowhere on recovering the data, I recommend you download and prepare a bootable CD of puppy linux from here
http://puppylinux.org/main/Overview and Getting Started.htm
Burn to a CD, boot from it, and now you can rootle around your disk without any interference from Windows whatever.
Now to the future. Many experienced Windows users prefer to separate the Operating System and the Data onto separate partitions of the HDD. (Use Easeus free partitioning tool for that). This is because the OS partition can then be imaged with free imaging software (with for example Macrium Reflect free - and there are many others). Without your data being there as well, the image is small and quick to produce. If you do an image regularly, at least just after every monthly MS update) then whenever your PC throws a hissy fit, you can just restore the entire OS to it's former clean status of a week or so ago, and life carries on smoothly.
If you buy an attached backup drive (USB attached), you can put the image on there, along with images of your data too if desired, and you have a good chance of being able to recover your life story even if your HDD completely fails you.
Sorry it's a long story, but if I am not speaking to the converted, then you probably now have a lot of food for thought.
