>>>>it has got slower and slower, mainly because of the the music and photo i have stored on it.
Storing lots of music and photos on your laptop will not slow it down. Files like that just sit there on the disk and have no influence on performance one way or the other.
Did the computer come with a hidden recovery partition?
Many laptops come with an image of Windows stored on a hidden recovery partition. By selecting this partition during computer boot up you can use it to reinstall Windows.
Have a look on the documentation that came with the computer, or look on the Dell web site on their support pages.