Wi-Fi keeps disconnecting and being extremely slow?

We have a 'main computer' in our living room which has the Comcast internet connection. Then, we also a have a Wi-Fi router that's from the brand Cisco. We have an iPhone, iPad, a laptop, and another computer upstairs. It seems for about 1-2 weeks, the Wi-Fi is working fine, and it has good speed. And then all of a sudden, it doesn't work, or is extremely slow, and doesn't load anything. Before, I used to press the reset, or refresh button on the router, and disconnect the cords from it and put them back in. That USE to work, and now nothing works. Please help. Should we just buy a router that is better? Because I'm pretty sure that the router we bought is the cheapest, and basic router.

Basic or not, a router isn't supposed to drop out or slow down the connection intermittently. Just get one that actually works.