Lucky for us, Turbine has a very generous idea of "weekend". This one will run from Thursday the 17th until next Monday the 21st. All inactive accounts will be reactivated and given a +10% XP boost to help you catch up. Even better, you'll get to check out Siege of Mirkwood while you're there.
You won't need to do anything to reactivate your account, just log in -- Turbine has taken care of that for you. They haven't gone quite so far as to download the client onto your computer, thankfully. If you need to reinstall, you can take care of that here.
Enjoy the free weekend, and we'll see you in Middle-earth!