Sue, sorry to say this is a common problem these days. It sounds like there are several catalogs on your system and sometimes it's hard to know which is the right one (especially if they all have the same names).
I'd suggest doing a search from your desktop (Mac Finder or Windows Explorer) for "Lightroom 2 Catalog". (version one uses just Lightroom Catalog).
From the results list, one by one, double click to open each one until you find the correct one.
If, for some reason, none of these are the catalog you previously converted, find the most recent version of your v1 catalog and re-convert. But make sure you don't keep re-converting; this just means you're opening the wrong (old) catalogs.
Once you've figured out which is the correct catalog, get rid of all the others. You might also want to make a backup of your v1 catalog and then delete it, too.
Even doing so, occasionally when starting Lightroom it may try to load an incorrect catalog. Don't worry, your data is safe. Just keep track of your current catalog location and you can always select it manually if you need to.
And always maintain at least one backup of your current catalog, on separate media from the master.
Hope this helps, good luck!