victor-blr, have you tried using Mobileuncle tools? If not, please see this tutorial
[Only registered and activated users can see links Click here to register]
If that still does not work, please see post #6 in this thread.
If still nothing, then you have to restore an NVRAM backup if you have one.
If these still do not work, please check if you have a valid serial number. If not you will need to restore that as well. If you flashed a ROM, you need to find a corresponding modem database file and ini file for your chipset.
Make sure that you use the files that are compatible with your ROM.
Use this program
[Only registered and activated users can see links Click here to register]
Install and run the program as administrator. Under Options, select to connect into meta mode.
Click on Reconnect. While your phone is off, connect it to PC.
From the drop down menu on the main window, select Update parameter.
In the new window that pops up, tick Barcode at the bottom.
Click on Change NVRAM DB then select the database modem file (it should be named BPLGUInfo...something)
Click on the Load from file then select the ini file (should be specified to match your chipset, MT6582)
Click Download to flash, then check if your Serial Number is restored.
Hope it works, good luck