When you want to turn on the phone, do you see a red blinking light near infra port? If yes, then can be due to discharged battery(in this case fully recharge the battery using other phone), or can be a dead EROM. In this case check this guide: REPAIRING EROM GUIDES for most sonyericsson phones
warning: don't ever use db2020 security bypass.
There is nothing wrong with db2020 security bypass if you use it properly, otherwise...you see the result...

When you repaired your phone, then use one of unlocking guides. Here is mine: Remove SIM-lock patch generator. Follow it carefully