belated return

dear friends

i know that we can file our belated return with in one year from the end of assessment year but i want to know that if a person does not file his return in the above mention period then what will happen.whether AO itself can determine our tax liability after this period.whather we can file our return after this period is there any proviso.what are the panalities in this case.if suppose ITR related to refund then can we claim refund after this period.some similar doubts also plz reply.

thanks & regards

tarun rustagi