My xbox 360 hard drive has been really slow loading lately...?

it takes about a minute to load up the xbox guide, all games load really slow, and the dashboard always freezes for about 2 minutes when i turn the xbox on. Ive tried clearing the system cache, cleaning it up of unessarcy items, and not using it for a week or so, yet still nothing worked. When i take the hard drive out, it works just fine. So ive backed up some of the important stuff on a USB, but there still is alot left on that hard drive, considering its 250GB. My Question is, would running initial setup or formating the hard drive help at all, and would initial setup delete all my data?