Not filing your taxes may be seen as a tax evasion. This is the illegal non-payment or underpayment of taxes. Unless you have a reasonable cause for your failure to file timely or fully, you might be subjected to the failure to file penalty. If you were granted an extended due date and you do not complete or pay your return you may also be subjected to this penalty.
For more information on filing your taxes if you did not file tax return please read this article http://ez-online-tax-filing.com//what-to-do-when-you-have-not-filed-taxes-for-many-years.html