My sony ericsson g900 is restart auto after insert the SIM card. without SIM card not.

SOURCE: Locking my g900 sony ericsson with a pin code

Go to the 'Main Menu' > 'Settings' > 'Security' > 'Locks'
In the decide whether you like to set up a Security Code upon opening the phone.
If you want so, under the 'Phone Lock' category choose 'At power On'
If you want it to lock automatically when you're not using it,
check the box beside 'Inactivity Lock'
When your prompted to put a Security code upon doing those,
type in '0000', it is the default Security Code for this unit.

SOURCE: how to access internet using wifi for g900 sony

1.Activate wlan
2.Scan -search for WIFI
3.Those without lock u can connect to(the others need password more often a wep KEY)
4.Some of them requir to pay (so it is not locked but in order to have internet access you need to pay)
5.connect (if the wifi use dhcp it sends to your mobile IP address + gateway+ dns)
6.You check your ip anf if it is something like 192.168.x.x it should be ok
7.you try to open internet from the menu.

Good luck.

SOURCE: calibrate

go to main menu> control panel> general> setup wizard
click next untill pencabration comes