The fact you changed routers naturally lead me to believe the router was the problem, and presumably you too. However, re-reading your original post, you actually said everything was fine for a couple days, and then the problem started. That makes me wonder if changing routers was just a coincidence. And maybe it's a problem upstream, either the modem or the ISP.
So try connecting the PC directly to the modem. If the problem continues, then we know it's not the router and more likely the modem/ISP. If the problem stops, reconnect the router to the modem and try a wired connection from the PC. If the problem stops, then it probably is a wireless issue.
IOW, narrow down the culprit by systematically isolating the modem and router (both wired and wireless).