Kindly, if the DSL on you modem is working that is mean your your line is working probrly frfom ISP sit to solve this problem
1- check the MTU configuration on your modem
2-check your NIC, my be causes this problem, or the interface card even you work via wireless
3-check Tepm. File some time causes many problems
after that if you didn't any problems from this componant you should contact with ISP to change the connection for you , sometimes the WAN connection PPPOA,PPPOE ot compatable with the parameter of line .