HTC explorer internet problem?

so i got my new htc explorer today and since its a total internet and socializing phone so i decided to put a new sim card for a gud internet package . after i inserted the new sim in the phone i went on to activate it so i dialed the customer care center and had it activated ,after that they told me to put the gprs settings for the internet so i did as follows but then no internet connectivity :( i called them again but they just told me the gprs config again so i reset the phone and i put in the config again ,still nothing i have tried this several times but nothing happens , no mobile internet , the net was working on my older sim card which i had previously inserted into it but not on this one :( please tell me what to do is it the phone or the sim card ? Thank You