What's happenning to My x600

i have a samsung x600 phone.i have a problem with my phone. i cannot understand what happened. i have a simcard named AVEA. if i inserted it, it starts and nothing happened. But if i insert TELSIM or TURKCELL ( other operator sim cards), it starts and if network is found, it restarts or closes itself. but sometimes i hardly opened it and 2 or three minute later it shuts down. can it be ok if i will flash it? or a problem with unlock codes. i cannot understand. if problem is from unlocking, it cannot open other operators and closes itself 2-3 minutes later. please HELP!!!!

i cannot understand this damn thing. i severally did full eprom reset but i cant manage it to start. But now it is working about 2 hours. what is the problem,what is the shit about my x600