internet/wifi problems?

I have an xfinity modem hooked up to my computer. On top of that i also have a netgear router. I dont know why but i would have a really difficult time trying to connect to the xfinity wifi through my laptop. On my iphone it seems to work fine but still laggy and would takes a while for videos to buffer. The best option/wifi for me is the netgear router wifi but it would only work for a certain amount of time and then just disconnects and disappear from all the possible wifi options i could choose from. The xfinity wifi will still be available but it wont connect to the internet through my laptop. I tried restarting both the router and modem but same results. Whenever connected to the internet through my laptop, my top would disconnect a lot when someone uses the computer. I'm thinking the router might be the problem but at the same time not because the wifi from the xfinity/comcast modem dont even work most of the time. I really dont think it has anything much to do with where im placing both the router and modem because before it worked great when only the netgear wifi was available until my power went and restarted the modem. Now i just wanna throw everything out the window. Somebody know what the problem is it is reallly driving me nuts especially when paying over 200 dollars a month for this crap.