If you have an EIN, you will need to file a return.
When you apply for an employer identification number (EIN), the IRS automatically determines what tax returns (income tax and employment tax) it expect that you will file. If you do not file all returns as outlined in the acceptance letter received about your EIN, the IRS will start sending you notices and may assess failure-to-file penalties.
If you need software to file your 1120 (or 1120-S), you can find TurboTax for small business at https://turbotax.intuit.com/small-business-taxes/
Note: Not-for-profit (tax exempt under section 501) organizations are also required to file returns every year, or risk losing their exempt status.