Serious TREO problem Please help!

Hi

I was desperately hoping somebody here could help me with my problem. I bought a new Treo 600 5 weeks ago off Ebay in the UK. It was locked to Orange. My plan was to us a Pay as you go card (Prepaid) with my cell phone. It never worked! I used the tool yesterday to unlock my cell phone and then my Treo 600 worked with my prepaid card and I was able to phone a friend. But today it is not working and not on my other 4 prepaid cards (all different networks). I have tried several times even reinstalling the ROM update. Essentially what happens is that my cell phone does not find any network it will also not let me search for other networks it just crashes. All it says is no service. Does anybody out there know what the problem is I want to use this phone so much! THX Pedro