Depends on what exactly you did. Did you format the drive when you installed Windows? If not, all your files will still be there. If you formatted the drive then installed Windows, you may be in trouble. You can run Recuva or another file recovery program to see if it will pick anything up to restore. You should do this with your drive as a secondary in another computer that is running the program. The more you use your drive, the less chance there is of getting files back as your old file locations are over-written. That is why installing Windows over a wiped drive is really bad for file recovery, the Windows setup can easily over-write your files.