You don't need to reload your photos, you just need to find and open the correct catalog. Search your computer for files with the extension .lrcat.
You can also set the catalog preferences to open a specific catalog every time you launch Lightroom. Read both of these and it should answer your question.
Thanks Theresa I did find a more recent catalog however it does not contain the photos I was working on yesterday - those files are (thank goodness) on my wireless hard drive but I do not know how to reload them back into Lightroom - I am hoping not to lose all the editing that I did as they are from a wedding where I have edited over 100+ photos - the xmp files are in the hard drive next to the raw files but I am unsure as to how to get them into Lightroom without losing them - thanks for your help I'm trying not to lose hope
I did find a more recent catalog however it does not contain the photos I was working on yesterday - those files are (thank goodness) on my wireless hard drivebut I do not know how to reload them back into Lightroom
As Theresa said, you don't want to, and should not attempt, to re-import the photos. This is a very bad idea. Don't do it.
You need to find the proper catalog file. Use File->Open Recent and open each catalog listed there.
If you don't find the right catalog that way, then have your computer's operating system do a search to find all files on all hard disks whose name ends with .LRCAT. Open each one by double-clicking on it until you find the right catalog.
And if that doesn't find it, then you have to restore a recent backup of your catalog file. You are making regular backups of your catalog file, aren't you?
The best option is to find the correct catalog, the one that had all the edited images in it. If you can't find the catalog, and your only option is to reimport, you will be okay because the xmp files are there. When you import the images, Lightroom will see the xmp and automatically import that data too. This means your images will import into Lightroom with the edits applied.