mobile

when I was browsing suddenly my phone switched off , I coudnt turn it on. I changed battery, tried charge but no hope. but I noticed that when I press and hold power button a red led light on top starts blinking. and nothing happens. I send it to repair. but they coundnt find any problem. even if I press any button screen is dosent turn on. it looks like brick. any one have any idea how to fix it.