"the other computers work with the same modem."
Your post was rather hard to read but I do see where (but not what) the problem is. Since nothing was told of said PC or Mac there is little to be offered except to replace that PC.
about a month ago my internet connection didnt work for some reason, i don't know. when the problem started, i tried to hook up with another LAN cable and it works fine. looks like the only problem was with the cable in my room. when the problem appeared, i used troubleshoot from the MSN messenger to look for the details and it said something related with the default gateway. after that i thought it was because of the operating system so i format the whole system. but it was no use. i install the program Magic Network, where when you cant connect they will show you step by step on how to fix it. first was to pull off the power cable from the modem for 5 min. and connect it again. but it didn't work the second step which was related to a rotor but there was no rotor so i just ignore it. I also called the ISP server provider but they gave me the same answer as the Magic network and try with another LAN cable from the modem which worked fine and i thought it was fixed but later on when i returned to my room the problem still coexist. now I'm wondering if there is any program I can use to fix it or any other solution other than using the repair icon from windows to fix it (which didn't work at all) right now i'm just guessing that there might be a problem with the modem but still the other computers work with the same modem. if anyone can help me with this problem i'd really appreciate it. thanks for the help.