Sony Xperia Z1 can not detect Sim Card problem occure when sim card port dammage or points brake on mobile circuit board. We can troubleshoot this issue with simple steps. Confirm that sim card is ok or check mobile with other sim card. Second reset mobile settings and check mobile Aeroplane mode is off. Stil mobile not accepting sim then disassemble mobile and check sim card holder jacket with multi meter, check each point related to jacket and apply jumper if any point is missin as shown diagram below.
Note! Every Hardware related solution here checked at least one time by us.Try these tricks on your own risk. We are not responsible if any damage comes to your device during the hardware repairing process.