Win7 files/folders created having wrong datestamp ie always 03/02/2000

Using Windows 7 64-bit NTFS system, backing-up files to a 1TB drive connected to wireless router.
Up till 05/02/2011 everything was fine when creating files & folders on the USB drive, now have noticed that ANY files or folders created on the USB drive has a date stamp of “03/02/2000 23:46”, anyone got any idea why this is happening please, and also how I can resolve the issue, I’m now having to create backups with filename containing date & time stamps.