Which version of Lightroom are you using?
All your Presets can be found in the locations below on your computer:-
• Mac (user)/Library/Application Support/Adobe/Lightroom/Develop Presets
• Win (user)/Application Data/Adobe/Lightroom/Develop Presets
If you updated from 5.x to 6.x/cc, check your preferences to see if you have your presets "stored with the catalog".
The 5-to-6 upgrade created a new catalog for you.