I need help in locating my backups

I have HP model a6863w. running vista home premium 64 bit. I have a weekly backup to an external hard drive. I make manual backups frequently. When I go to the external hard drive I can locate my manual backups, but cannot find the weekly scheduled backups.

They may be incremental backups...meaning they add only changes to existing backups...
You didn't mention what app you were using for these...

As the prior poster has mentioned, they are probably incremental. You will not see individual dates. With some back up systems the only date shown is the earliest. Changes are made to that backup.