After long hours of working, my router becomes non-responsive. What should I do ? More info is given below.?

Try clearing dust from the router, a vacuum cleaner pipe on the vents should clear most of it and I have heard this resolve issues for some people. Have you got the router running the latest firmware? It is possible this is a known issue that was resolved. Try to keep the router clear from other electrical items, I have had a router crash constantly when running in a server room because of the other equipment. Lastly I would suggest just investing in a new router, a bit of a cop out but sometimes better than troubleshooting for ages.