What will happen to your computer files if you format?

Unless you back them up your going to lose them. Id recommend you back them up to an external HD. Once you format your computer everything is lost, all your files, all your settings, everything is gone.

Though if your only formatting to get rid of private data, don't just assume its gone for good. Youv'e just made it a tad harder to get them that's all. But generally speaking, format your computer and you have lost everything.