Why does my router keep resetting?

so basically whenever i play xbox online in the early morning(before noon) or at night(after midnight) my wireless works fine.. i think its because theres almost no connections at that time. but in the daytime if i play xbox the router will just reboot and i will get kicked off xbox live until its fully restarted. sometimes it will take 5 seconds to reboot sometimes it takes a few minutes. and whenever i do sign back on it will reboot again soon after that usually within 5 minutes. most of the time in my house there are 2 wifi phones 1 wifi ipod a wifi laptop and my xbox and wii. thats usually around 6 or 7 when everysingle one is trying to run and the wireless just drops and comes back on. i have no idea why this is happening because my router should be able to hold at least 20 wireless connections at any time. will someone tell me why it is doing this? please help!!