Restoring back to original Vista

Hello,
I seem to have a messed up Vista system and want to Restore everything back to the way it was when I bought the HP Pavilion. My first problem was when I attached an externat hard drive. It was then the "J" drive. Everything was okey. Then one day it came up as the "F" drive and since then I cannot edit and save anything that I have on the drive. I do a lot of HTML and JAVA programs and now I can't update them. Also, the system seems to be running veeeeeeery slow. I tried cleaning my Registry but that doesn't seem to help. I will be the first to admit that I am not very good understanding the inner workings of a home computer, so if anyone can help me fix my problem with the F dirve and tell me how to get all the junk off my computer with/without a system restore, I would reeeeeeeally be greatful.

Thanks,