You go to the folder that contains the catalog file (it's name ends with .LRCAT)
In that folder is a file whose name ends with .LOCK. Delete this .LOCK file. Do not delete anything else.
If you see a .lock file in the directory that contains your Lightroom catalog then delete it. Information of the default location and name of the lock file is shown here:
Catalog lock file
C:\Users\[user name]\Pictures\Lightroom\Lightroom 4 Catalog.lrcat.lock
Note: The lock file prevents the catalog from being overwritten when in use.
Use Windows Explorer to open the folder containing your Lightroom catalog. By default it is in Pictures\Lightroom. In that folder you are likely to find a file with the .lock extension. After you delete that file Lightroom should start normally. This log file is generated by the Lightroom catalog whenever Lightroom is started. It is supposed to be deleted whenever Lightroom closes. But if things don't close normally it can sometimes be left behind
Thank you all for your help! I finally figured it out, kept going into the wrong folder - yeah, sometimes the simplest things can make one feel so technically challenged! After a few tries finally looked in the right folder (Pictures instead of Adobe!) and voila! there it was! All fixed, ready to resume editing photos, am a happy gal now! You guys are awesome!