Windows 8 has set some file types to open in full screen Metro applications which can be really annoying, especially if you just wanted to have a quick look at a photo or something. To stop this, you can determine certain applications to open all types of files they are able to open (e.g. Windows Photo Viewer for picture files - jpg, png, etc.).
To do so, hover your mouse over the top right corner to open the Charms menu and open the Search charm. Enter default programs into the search bar and open the search result with the same name. In the appearing window, click on Set your default programs (the first menu option).
In the new window, select one of the programs on the left that you want to use as general default options for pictures, videos, music or another type of files and click on Set this program as default afterwards:
Your files will now be opened in comfortable window applications!
The programs that are run on system startup are managed in a special application on Linux. Open Startup Applications from the distribution's main menu to find a list of programs already being run everytime you log in - you have the option to enable or disable existing entries, edit or delete them and to create new ones - click on Add to do so.
A new window with three text fields will open:
Name: Enter the name of the entry that will be shown in the previous menu.
Command: Enter the terminal command that launches the program you want to start - to see if you got the correct one, test it in a terminal (e.g. firefox, nautilus). If you want to start a program with root privileges, append the gksu string before the program's name (e.g. gksu nautilus).
Comment: Enter the comment that will be shown below the name in the previous menu.
Click on Add afterwards and close the startup applications window. Reboot your machine to test the configuration.
If you have ever tried to set another default application for opening file folders on Windows XP and to turn it back afterwards, you will have run into a really nasty bug.
If you try to restore the default settings of an application to open a folder, the folder will no longer open as before (normal explorer window, further folders open in the same window) but will open a search window on doubleclick.
You cannot achieve the former behaviour by trying to reset it in the control panel. What you have to do is to create a new opening action for File Folder and set it as default. Afterwards, open Run... and enter regedit to open the Windows Registry. On the left side of the registry, there is a list of directories. Browse this list to HKEY_CLASSES_ROOT > Directory > shell and click on the plus-button next to shell to unfold the actions to open file folders with. Now look for the new opening action you have previously created and set as default. Rightclick it, choose Delete and confirm your choice. It is not enough to delete this entry in the Control Panel, it has to be done in the registry. Close the registry after deletion and try out doubleclicking a folder. It should now open like it usually used to.
The default application is the one you open a file with on doubleclick. In some cases installed programs automatically turn themselves into the default application for files you were happy with, which you might want to change. To do that, rightclick a file of the chosen format and choose Open With... -> Other Application or Open With Other Application:
On the window that opens, choose an application or command and check the Remember this application for "..." files checkbox to apply your selection for all files of the same format:
Hit Open afterwards.