Is the problem with my computer, modem or my router?

I have a cable modem located upstairs attached to a Belkin router for my internet service. I have a desktop downstairs and a tablet wherever I want it.
At least once a day I lose internet service on the desktop (it is less that three weeks old) and have to go upstairs, unplug the power cord from the router and plug it back in. When I do this I, once again, have internet downstairs. My wifes tablet will occasionally do the same thing but much more infrequently. One other detail, I have an older computer (about 7 years old) upstairs that is hardwired into the router and it never loses service.
So, is the problem in the computers, the router, the modem or the cable service itself?