very little information to diagnose your problem.

Anyway, from your explanation it seems to me that your router is uanble to renew the IP address. May be the address has expired in 2 hours and unable to renew it. Restarting router is again issuing the DHCP to discover  IP address. Just login to the router to see if it has acquired the IP address when you find that router stops working (disconnected as you stated).

If its the problem, you can either put static IP address. If the same thing happens when you connect to laptop or pc instead of routing via router then call your ISP and explain them your problem. May be they can help fixing the problem at their side. If its only with the router then try resettting the router and reconfigure it (I can't suggest any other detail steps than reseting the router without knowing the details). If it does not work then before buying the router try upgrading the firmware.

Well, the problem may be other things as well. Its difficult to suggest anything just stating that router gets disconnected in every 2 hours.