Try one of the following
Hit Alt-F2 and enter gconf-editor. When the Configuration editor comes up, expand apps and scross down to nautilus. Expand nautilus and click on preferences. On the list to the right, check the box beside media_autorun_never. This will disable the autorun prompt for all inserted media.
or
1. In Nautilus, go to Edit > Preferences. Go to the Media tab.
2. Uncheck "Never prompt or start programs on media insertion".
3. Check "Browse Media when inserted".
4. Open the Gconf editor (Atl + F2 and type gconf-editor)
5. Navigate to Apps/Nautilus/Preferences.
6. Edit the "media_autorun_x_content_ignore" key and remove all entries.
7. Edit the "media_autorun_x_content_open_folder" key and add "x-content/software" to the key
8. Close the Gconfig editor.