I would HIGHLY recommend you seek professional help to get this matter resolved. If your owing $4,000 in 2006 was due to an error on your part, they can resolve that issue and you would not owe anything that was in error (unless you got $4,000 back that you were not eligible for, then you will of course still owe that). If you have submitted returns for the following years, that were correct, then there should be no more issues. If there were errors on them as well, then they w ill need to be amended. Each year will be a different return and a different cost.
Do not fail to file simply because of this issue, though. The longer you owe the IRS, if you do owe, the more fines and interest fees you will incur. Go ahead and get help with this years return, and let them offset any taxes owed from your return you are expecting to get. You have to pay it back eventually anyway.
They can and will set you up on a payment plan, and you can avoid legal trouble if you did not commit fraud. Be sure to have your records for the last 7-10 years on hand. Because of your past troubles, you are more likely to be audited.
Again, do not just fail to file because of the issue. It wille ventually catch up with you, and they could end up garnishing wages, bank accounts, etc. Cooperate with them. They are a powerful entitiy, which makes them scary, but they are NOT the enemy.
I would definitely seek professional help. Not being mean, but your admitted mistake trying to do it yourself is what started the problems...and it has continued. Seems logical that getting professional help would be the best idea as opposed to continuing the cycle you have been on for the last four years.
EDITED TO ADD: The tax professional might suggest you submit the amended returns for years past before submitting for this year, that way this years is not automatically flagged. Get started TOMORROW, though.
I wish you the best!
Common sense and research
Personal experience and opinion
Mom of three + one on the way!