kea4yank,
Consider the following:
*_Previous Time Machine Backups Are No Longer Visible_*
There are several reasons why this might be the case. Consider the following:
If Time Machine can successfully launch into its’ “time travel” interface then the software is seeing backups. It you only have two time travel windows to chose from, “Today (Now)” and a single window behind that, then Time Machine has only performed its initial full backup. You can verify this by looking at the time scale on the right. If no dates appear other than Now and the date of your first full backup then subsequent incremental backups have not been taking place.
If it has been MORE than an 1 ½ hours since the first full backup completed, then you need to determine why Time Machine has stopped backing up. It might simply be that the Time Machine Preference has been turned off.
If, on the other hand, you look at the time scale on the right and you see multiple dates going back to the time of the first full backup, but they are grayed-out, then Time Machine knows that incremental backups have been taking place. Nevertheless, only the front most window “Today (Now)” shows content. Take a look at the Sidebar of the Finder window. Among the various Devices, Shares, and Places, what is highlighted/selected? If it is the Time Machine backup disk itself that is highlighted, then click on some other location in the Sidebar to make the former backup windows appear.
You see, the Time Machine “time travel” interface displays the historical backup state of what ever location is highlighted in the Finders’ Sidebar. Since Time Machine does not back itself up, then there will be no historical backup windows visible.
Bear in mind as well, if you have added locations and items to the Time Machine “Exclude From Backup” list, then there will be no visible history of these items either if they too are highlighted or selected.
And of course, if you are looking at a file or folder that has only recently been created, then there will not be many, or any, backup copies of it depending on how long ago it was created.
*Anti-Virus Software*
If you have anti-virus software running try disabling, launch Time Machine again, and see if you can access previously backed up data. Sometimes such programs scanning processes can interfere with Time Machine.
*File Vault*
Does the User Account in question happen to have File Vault active? In another thread V.K. stated: "if you start TM from a filevaulted home directory all you'll see is present. you could browse your old backups of files outside your home directory but not anything in it."
*For Time Capsule / AirDisk users*
If you are backing up to a wireless device, and you have the Time Machine backup disk image (sparsebundle) mounted on your desktop while you are trying to access it via the Time Machine "time travel" interface, you may not be able to see any files from previous backups.
You see, if the backup disk image (sparsebundle) is already mounted on the desktop (a White drive icon) then Time Machine may conclude that the disk is “in use” and fail to mount it properly. Obviously, this is not a factor when backing up to a locally connected drive.
*SideBar is Missing / Can’t Navigate to Other Locations*
It may be that you see no backup history because the current window displayed
HAS no backups. Nevertheless, there is nothing else to choose as the SideBar on the left is missing and won’t allow you to select another location on your Hard disk to explore.
Cancel out of Time Machine on the left.
Back in the Finder, go up to the “View” menu.
Select “Show Toolbar”. The Sidebar should now be visible.
Choose another location to begin exploring backups.
Now click the Time Machine Dock icon to enter the “time travel” interface again.
*Reselect Your Time Machine Disk*
Go to System Preferences --> Time Machine.
Use the slider on the left to turn “OFF” Time Machine.
Click the "Change Disk..." button.
Select "None" and click "Stop Backing Up".
Now click "Choose Backup Disk" and reselect your backup hard disk again.
Now use the slider on the left to turn “ON” Time Machine.
Close System Preferences and try viewing previous backups again using the Time Machine interface.
Let us know if the above helped.
Cheers!