My internet keeps randomly disconnecting?

Every now and then I'll turn on my computer and for some odd reason my internet will , after 2-5 minutes, randomly disconnect and then reconnect after about 30 or so seconds. This continues for about a day or so, and my internet will be fine the next day. This can be extremely annoying when I'm playing XBox Live or something so I'd really like an answer. I have WPA2 security and constantly run spyware doctor and vrius scanning programs and such, but it still hasn't fixed my problem. I've also tried rebooting my router and modem, and even shuting down my entire computer, but still nothing works. My router's DSL light just starts blinking and my Internet light disappears and then reappears after about 30 seconds. Please help me.