So you are using the USB cable that came with the 2nd gen shuffle (it has a mini-dock on the shuffle end), correct?
When you connect the shuffle, you said the the orange light on the shuffle comes on. Does it blink initially (or continuously)? If you connect the shuffle with iTunes NOT running, and run Disk Utility instead, does the shuffle's disk appear in Disk Utility's sidebar? You can also try running System Profiler to see if the shuffle is recognized as being connected to USB.
There is no (practical) limit to how many supported devices can connect to iTunes at the same time (or separately). There is a limit to the amount of power available on the computer's USB bus, so connecting all FOUR of your devices at the same time may be a problem. But just the shuffle by itself should certainly work.
You've probably ruled out a software-related problem on the Mac (OS and iTunes) because your other devices work fine. You've ruled out a problem with the USB port being used; I assume you have used the same port to connect both the 2nd gen shuffle and your other devices. The remaining possible causes are faulty USB cable (the one used with 2nd gen shuffle) and a problem on the shuffle itself.
When you leave a lithium-based battery fully discharged for an extended period (like one year), it can become unable to hold a charge. However, I think the shuffle would still appear in iTunes when connected.
If the shuffle is seen by the Mac (such as in Disk Utility or System Profiler), but not by iTunes, you can try using this "reset" utility.
http://support.apple.com/kb/HT1238
