Sounds like I've got the same problem. I frequently have to reset my modem on account that it just stops feeding an internet connection. My computer will still recognize a connection to the modem and the modem will still have an internet connection, but somewhere in between, I lose internet access.
It seems to be spontaneous when it cuts out. Some days I can go without resetting, but I've had worse case scenarios where I've had to turn the modem off and on as many as twelve times throughout the day. Every time I turn it back on, it starts working again. I didn't have this problem with my last modem (it presented other problems), so I assume it's just the hardware in question; that is, if any of this relates to what you're going through.