Recently something happened while I was using my computer, which has windows 7. I clicked "documents" and went to the screen with documents. On the upper left of the screen is "Favorites" and below is "desktop", "downloads" and "recent places." However, I must have hit some key and suddenly these three categories disappeared. Now there is only "Favorites" with nothing below. Does anybody know what happened and how I can get these three categories back on my computer screen? 

My Computer
- Computer Manufacturer/Model Number
- HP Pavilian p6523w
- OS
- windows 7 home premium
- CPU
- Athlon II X2 220 Processor 2800 mhz
- Memory
- 5.00 gb ram