Is this a wired or wireless connection? If wireless, can anyone else connect successfully?
If you didn't do any settings manually, then it is possible that your router is set-up incorrectly. If your router is from comcast, then you should contact them and have them sort this out for you since they were the ones that made the error most likely.
If that doesn't solve your issue, then here are some things to try:
----------FIRST, BEFORE ANYTHING ELSE: CREATE A RESTORE POINT!-----------
Start with opening a command prompt and entering each of the two lines below, pressing enter after each one:
ipconfig /release
ipconfig /renew
... and see what happens.
If no luck, do this next:
Open a command prompt as an administrator (right click > run as administrator) and enter this:
netsh int ip reset
... press enter. Enter this:
netsh winsock reset
... hit enter, restart the computer and see what happens.
If this doesn't do it, there is a slightly more hardcore reset protocol:
netsh int ipv4 reset reset.log press enter
netsh int ipv6 reset reset.log press enter
netsh winsock reset catalog press enter
... Enter each line in an elevated command prompt (run as administrator) and press enter after each line.
Restart the machine and see what happens.
If you still have problems after all of this, please let me know and we will go from there. I am betting heavily on the mismatched gateway at this point. Even if there is another problem, this still needs to be fixed.
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