have you got the settings for a start?
try insert a empty credit pay as you go 3 sim card and see if you can acess skype?
download skype using 3's network, usually if it doesnt work its because you loss the certificate (*apparently*) to reinstall that i reckon you have to reflash it to 3's firmware.
note thats only due to your unbranding... (because whilst you was unbranding you probably wiped out the certificate hence the error)

according to 3 website skype is totally free for your handset
Skype