Phone Unlocking Siemens c35i - IMEI blocked??

[PostModernKarma]

I recently got a siemens c35i as a 30 day hire phone while mine was been repaired, (a sagem of all things) I decided i was going to keep the phone but after about 45 days the phone displayed the message "please insert simcard". I've tried numerous simcards but to no avail - can they block an imei from being used and if so can i unblock it.

Thanx in advance