I'm a novice in GIS.
I'm using QGIS 2.0.1. (Dufour) with Mac OS X (10.6.8). I have couple of dozens(?) of vector layers added on a project. At some point, when I opened a project, application opened a window "Handle bad layers". As far as I know, this should pop up when the project cannot find the file due to its new location, for example. There were a few (ca. 5) layers listed. But in the columns "New file" and "New datasource" there were the same path and file name. When I tried to select a file from the list and relocate it, QGIS crashed. After that it crashes every time at the same point. If I close the window, it's possible to get ahead. QGIS removed those files (vector layers) from the project's "Layers" list. That's not too bad. But now all the other layers in the project are empty.
- If I right-click one of them in the "Layers" list and choose "Show feature count", it shows the right number, for example . But the style definitions under it (I've made the categorized color style according to one attribute value of the data), it shows  as feature count value.
- if I choose "Open attribute table", it's empty. When I checked size of the original file (added as vector layer), it has some data.
I have NOT changed the location of data files - some earlier QGIS backup project files still find them. Am I having too many layers, perhaps?