Error 13014 and -50 preventing all functionality

Have you tried running activity monitor before going on itunes to whats going on there?, go on itunes get the error and close down itunes via activity monitor and see if you still can't perform tasks, also how have you repaired the permissions, via holding down CMD+R and repair permissions on the disk utility there or via the system preferences?

Please read this whole message before doing anything.

This procedure is a diagnostic test. It’s unlikely to solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.

The purpose of this exercise is to determine whether the problem is caused by third-party system modifications that load automatically at startup or login. Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards. Boot in safe mode and log in to the account with the problem. The instructions provided by Apple are as follows:

• Be sure your Mac is shut down.
• Press the power button.
• Immediately after you hear the startup tone, hold the Shift key. The Shift key should be held as soon as possible after the startup tone, but not before the tone.
• Release the Shift key when you see the gray Apple icon and the progress indicator (looks like a spinning gear).

Safe mode is much slower to boot and run than normal, and some things won’t work at all, including wireless networking on certain Macs.

The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.

Test while in safe mode. Same problem(s)?

After testing, reboot as usual (i.e., not in safe mode) and verify that you still have the problem. Post the results of the test.

Your boot drive seems to be malfunctioning. You might be able to fix it, at least temporarily, by backing up all data, erasing the drive, and restoring from a backup. If that doesn't work, take the machine to an Apple Store or other service outlet for testing.