HELP ME PLEASE

HELLO ! I NEED SOME HELP WITH MY TOUCH DIAMOND. IT WONT CONECT TO INTERNET (BY WIFI OR BY GPRS/3G ) THE ONLY WAY I CAN USE INTERNET IS TO USE THE PHONE AS A MODEM BY CONECTING IT TO MY PC. IT CONECTS TO WIFI OR 3G BUT WHEN I TRY TO OPEN THE INTERNET IT SAYS "CANNOT FIND SERVER OR DNS ERROR". PLEASE SOMEONE HELP ME I DONT KNOW WHAT TO DO.
IM NOT A COMPUTER GENIUS SO BE SIMPLE GUYS  (SORRY FOR ANY MISTAKES BUT ENGLISH ITS NOT MY NATIVE LANGUAGE)