First thing I would do; reboot computer, then make sure you have all MS updates, then update ethernet driver. Next I would run a Virus scan, then run scans for malware, spyware and adware. Then reboot again and check internet connection. Then reset modem, unplug it from outlet for 30 seconds and plug back in. If that doesn't work then I would do a system restore to a point in time when you had no issues. If all else fails a complete reinstall maybe in order.
Question; when you installed wired router did you load and run installation disc that came with the router? What brand of router?