No you can't start claiming depreciation now without a change in accounting method. This is because the IRS considers an error for two years or more an adoption of an accounting method.
You also will want to make up those missed years, because when you sell the property, you will have to recapture the depreciation you should have taken.
You can calculate the difference in depreciation and prepare the proper form, 3115 in a Desktop version of TurboTax.
