I understand that modems crash and all of that, but today my cable modem wouldn't connect to the Internet, it "froze" for hours.

Get it replaced.

What is the average life span of cable modems anyway? I already had to replace the one my ISP Charter gave us. Didn't really work from the start anyway though, but I occasionally have the same issue as >>1. I just unplug it and leave it for like 10-15 mins then it works just fine, assuming Charter has the connection up long enough.