Were you trying to import your Favorites from another browser? The way
to do this is with the Import/Export Wizard in Internet Explorer.

Otherwise: Do you have any clues as to what caused your Favorites to
suddenly disappear? Were you making any adjustments to your settings,
perhaps? Using a registry cleaner, maybe?

If you can't think of anything you or someone else might have done that
would cause this to happen, you should thoroughly scan your system for
malicious software with /several/ of the better online scanners
(Kaspersky, Eset, Trend Micro, Panda, Sophos, Symantec etc.) and, if
necessary, submitted a HiJack This log to one of the expert web sites
that analyze these logs.

Installing a fresh copy of Windows won't get your Favorites back.

---
Leonard Grey
Errare humanum est