It is always a good habit to file your taxes in order to avoid a tax lien being used against your property. But if you fail to pay, regardless of how ugly or hopeless the situation may be, there is a chance to fix it, and sooner the better.
Whatever documents you can get your hands on, file it. However, if there is a lost paperwork, try to ask for an extension and request the IRS for transcripts. You can also do this via the internet if you are uncomfortable going to the IRS.
The next thing to do is apply for a payment plan. Do this in order to save your assets and property from being sold to auction. If there is an opportunity though, negotiate for a reduced amount of the debt, or ask for help from a tax expert lawyer.