SIM card is not working on Sony Xperia Z (Android 4.1.2) My friend has a problem using his micro-SIM card on his new Sony Xperia Z (Android 4.1.2)

The problem is: when he inserts the SIM card, the phone display a message that the SIM card has been inserted, and restarts... then after the restart, displays 'SIM card removed' and restarts!

Notes:
1-The SIM card works perfectly on other phones.
2-The shop where he bought the phone has installed apps (mostly games) before he received it.

Any solutions?
Can you take a look at the SIM and phone SIM socket if they are oxidized/dirty/greasy?
If that is the case, you can clean it with a cotton cloth dipped in ethylene alcohol.
If the SIM socket pins are somehow are pushed down, that could be also an issue.