Confused about TM's 'grey' & 'purple' horizontal lines in timeline

Question

I have Lion OS 10.7
Whenever I connect my LaCie external HD and click on TM, the Star Field timeline would show both Grey and Purple horizonal lines.
Grey horizontal lines being TM's Snapshots
Purple horizontal lines being my external HD
I just downloaded software from the Apple and when I enter the Star Field, there are no grey horizontal lines.  If my LaCie is not connected, a pop up box says that my 'TM backup disk can't be found.'
But, I have entered the Sar Field in the past without my LaCie connected and there used to show about a week of TM snapshots, all grey horizontal lines in the timeline.
Has something changed?  Is TM snapshots still taking place when I am away from my external HD?  
Thanks for your help,
B.

Answer 1

You're saying you select Enter Time Machine from the menu bar and nothing happens? If so, proceed as below.
Please try each of the steps below that you haven't already taken.
Step 1
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the page that opens.
Click the Clear Display icon in the toolbar. Try again to enter Time Machine. Post any messages that appear in the Console window – the text, please, not a screenshot.
Step 2
If you're backing up to an external hard drive attached to your Mac, open the backup volume in the Finder. You should see a folder with the name "Backups.backupdb". You should not see a file with a name ending in "sparsebundle". If you do see that, the backup was created over a network and can only be used that way.
Step 3
Launch Disk Utility and select the icon of the backup drive in the pane on the left (not any of the volume icons below it.) At the bottom of the window, you should see this:
Partition Map Scheme : GUID Partition Table
If the partition scheme is anything else, the drive has to be repartitioned (with the loss of all data.)
Step 4
In the Finder, select Go ▹ Go to Folder... from the menu bar, copy the text on the line below into the box that opens, and press return:
~/Library/Preferences/com.apple.finder.plist
Move the selected file to the Desktop, leaving the Finder window open for now.
Relaunch the Finder by selecting  ▹ Force Quit... from the menu bar, then selecting Finder and pressing return. Your Finder settings will be lost.
Try again to enter Time Machine. If you still can't, put back the file you moved to the Desktop, replacing the newer one that will have been created in its place.
Otherwise, close the Finder window you opened and delete the file you moved to the Desktop. Recreate your Finder preferences.
Step 5
Boot in safe mode by holding down the shift key at the startup chime. Try again to enter Time Machine.
Note: If FileVault is enabled under OS X 10.7 or later, or if a firmware password is set, you can’t boot in safe mode.