I have seem to have lost my solidworks file. But I have my STL file.
When I bring it back into SW I can't measure anything or convert to a format that is usable?
Not easily, so your best option is to rebuild it since it is fairly simple.
If it was something you put a lot of time into and the STL was relatively high resolution, there are some high end tools like Geomagic that can build nurbs surfaces from the STL. The software is expensive, so you would probably end up paying a service to do the conversion if you have to go that route.
Retrieving data ...