BELFAST (Reuters) - Irish nationalist party Sinn Fein said on Wednesday that its talks with the pro-British Democratic Unionist Party aimed at re-establishing a power-sharing government in Northern Ireland had failed.   Sinn Fein is disappointed that after the last few weeks of negotiations that it has ended in failure,  Sinn Fein s leader in Northern Ireland, Michelle O Neill, told journalists.  We did our best to be flexible.  She called on the British and Irish government s  to act urgently to deliver equality  in Northern Ireland following the failure of the assembly to deliver it, citing the terms of the 1998 Good Friday peace deal.  