i had an s2 sitting in the house for a few months so decided to pass onto a friend...the phone was unlocked as from car phone warehouse and was in perfect nic when i used it..when friend puts sim card in for tesco mobile the phone shuts down so thought try another sim but even with a gifgaff sim the same thing happens...just hoping han get some help to solve issue..cheers for reading

That's not normal.
I would go back to car phone where house and ask there ?
There could be a problem with the unlock. (Unlikely but bugs can happen).

What happens if you boot the phone up with out a sim card in it?
Yes you will get no service but you need to work out if its shutting down because say the battery is faulty and giving you the wrong reading ?

Hope that helps.

only shuts down when put a sim card in as far as i know will double check later...phone 2 years old now as was my old contract 1 was not locked to a network being from carphone warehouse