Lenovo a850 problem with SIM card undetected because missing of Imei and baseband info lead to comm failure.
Even though SIM card is inserted, but notification remains with SIM card not inserted
Cause of the problem
User said it suddenly happened after he changed SIM card
Corrupted nvram may cause from system update or suddenly remove simcard so that as a precaution turn off handphone before removing the SIM card to ensure system data were not affected or corrupted and if any ongoing system update do not turn of handphone until everything complete. Also do not remove the battery while the system still running, shut down the system via the off button first then remove the battery after the completed turn off.
Root your phone via framaroot
Install ROM toolbox lite from Google Playstore
And delete nvram folder inside ROM toolbox lite on Root Browser : data/nvram
Before deleting nvram folder copy and backup somewhere first in case of software brick.
In 10 Secs SIM card will regain its signal, restart your phone,
Nvram folder will be recreated back
While SIM card will be detected again and can normally makes calls or data.
If you unable to do it, send your handphone to us, we will fix it for you with little charges. 0142871121