Must reset modem for internet access?

-So here's the deal: My router;s power supply went bad the other day, so i have to get a new one, but until then, i just plugged my ethernet cord directly into the modem. I have an xbox 360 and a pc, and any time i want to switch the cord from one to the other, i have to reset my modem or i have no internet, sometimes it works and sometimes it doesn't. im just wandering if anybody else has had this problem before, and if so, how did you fix it???unplug the power cord then plug it back in