Depreciation in schedue E?

I bought a rental house in 2003. but i didnot claim depreciation in 2003 tax return(a accountant did it fpr me).because i thought if i claim depreciation, after 5 years, it would be too much net income for taxes. but today i use TurboTax to do tax,it say IRS require claim depreciation, is mean i have to do it? Thanks for any respone.