Default Phone not booting (Is it soft brick?)

Hei,

I was running 4.3.1 Dirty Unicorns and wanted to flash Smartdroid.
So, flashed Devil recovery and tried to flash the ROM.
It gave me message that there's an error in the zip file.
I was just playing with the options available in the recovery and selected some option, which I don't remember now.
After that, the went into bootloop. "Samsung Galaxy S3 I9300" appears on the screen and the phone reboots again and again.
This loop continued.
The phone could be put in Download mode.
Then, I flashed CWM 6.0.4.4 and flashed 4.1.2, which I downloaded some time back.
It went on well. I could boot the phone and had set it up.
However, I couldn't connect to network.
The IMEI was some default one.
Rooted the phone and tried to restore the backup of efs folder using HC-Ktool.
After restore, when I booted the phone, it didn't boot.
"Samsung Galaxy S3 I9300" appears on the screen and the phone reboots again and again.
I tried flashing the ROM again, CWM again etc etc.
Nothing worked.
In one occasion, after installing CWM 6.0.4.4, I restored from NANDROID backup. Restore was successful.
But, it wouldn't boot.
Same "Samsung Galaxy S3" appears on the screen and the phone reboots again and again.
Once, I flashed Dirty Unicorns ROM from zip via CWM. Still the same.

What is happening and how to solve it?

Any help is greatly appreciated.

Regards,
Babloo