Got a new computer and, stupidly, Steam installed Skyrim. Now, also have Dawnguard and DragonBorn. There are no files
on my computer for Bethesda. Three questions:
1. How can I clean up my Saves (or do I need to, as all is on Skyrim)? I have 1170 saves.
2. Can I re-install Skyrim by my DVD or will that foul up everything I have done, and I will have to start over.
3. If I did re-install by DVD, what will have happened to my DLCs?
Any help appreciated.

(My )Documents/(My )Games/Skyrim/Saves is where they're stored. Copy and paste the saves from the other computer.

Yes, Skyrim will install fine from the disc.

They'll download when Steam updates Skyrim after install.

Thanks for the quick reply. Just looked there and no Skyrim/Saves. Unfortunately, don't have the other computer. It appears, as I suggested that
Steam has stored all my Saves. Could that be? (Totally confused)

Steam does not store all saves. It stores the most recent of a certain amount up to a size cap. If you want your saves, you'll have to get them from the other computer.

OK, thanks.