I have a Galaxy S3 i9305 that used to be rooted and installed with Cyanogenmod 10.1, but recently I decided to start anew and formatted everything in cwm recovery. Then, I flashed samsung stock rom android 4.3 (I9305XXUEML8) and gapps for 4.3, but the rebooting suddenly seems longer and the phone cannot detect a sim card, hence, no network. Moreover, there is no notification whatsoever when I plug the device into the com, except showing the charging notification light. It can also hang randomly after I turn the screen on. The phone is not rooted anymore and has stock recovery. I have a feeling this is because I formatted /modem or /tombstone. The phone is not very old so I believe it isn't a problem with the card slot or anything. Is there any way to solve this problem? Thanks a lot if anyone can help!