Can I connect a second modem to my network?

[Jan]

Had shaw as my isp before and thought of the same thing to better my experience. But in my case, I actually had another modem exactly the same as the one in use. Long story short, once i plugged it in with the original one turned on, did not work, so i though i needed to unplug the original one. defeating the purpose, i still unplugged the original one and tried the other one by itself; did not work. Seems like they actually lock your account to a certain modem through its serial number, because everytime i called they'd ask for it.
So that was my experience. BTW, why modem only needed its power cord and a coaxial input, then only one ethernet cable for output which was connected to the router.