Nokia C-7
Phone start up failed

My phone is troubling me vry much

it gets switch off on its on, hangs, n n now a days whenever i switch on my mobile it displays `PHONE START UP FAILED CONTACT THE RETAILER'

my phone is under warranty n i want it to be replaced..i have given my mobile 3 times to the nokia care but my problem is nt solved... this phone is troubling me so much...