not sure if this forum will help you out but have a look.
K800i inactive sim
plus found this on the internet.
it may be the software needs reloading, if you download the "sony ericsson pc companion" to your pc you can connect your 800i by usb lead, then click on the companion panel for updates, it will give you the option to repair phone, select this option and all your software will be renewed. or if you prefer to contact orange first just go onto their website and the phone numbers will be there.
U just istall p.c. suit of sonyerricsson and take backup of ur data,, then u need to flash ur handset from sony erricson service centre.
OR THIS MIGHT HELP.
sony ericsson k800i inactive sim problem Google Search