This should never happen, Cliff. Usually when you first open a new version of LR, it offers to upgrade the previous version's catalogue and so always keeps your keywords and other work.
So to resolve this, first open LR3 and go to Catalog Settings, General. This tells you exactly where your catalogue is stored.
Now close LR3, open LR4, and use File > Open Catalog to point to the above catalogue. LR will offer to upgrade it. Job done.
Once you're back on track, you really need to get the roles of catalogues clear in your own mind.
John