Aftermarket stereo power problems...please help..!?

i had my indash dvd hooked up for a yr it worked and played fine.. 1 day my car wldnt start and the radio wldnt turn on... i had some idle solenoid changed but til this day i even unwired and rewired my stereo and still nothing... i put my factory tadio back in and it works fine but wen i plug in the indash i get power for 3 seconds sometimes not even and then it shuts down... what could this be? why would it work for so long then jus stop n not stay powered for more then 2-3 seconds. it will just keep flickering like that i dnt have to press power.. its a 00 impala.. i got the harness for onstar.. i dnt even have onstar would i be able to use just a regular gm harness?