One thing to check is your connection settings.
Click on the signal strength icon, down by the clock, on your taskbar.
A sidebar should pop up. Right click on the item with your router name.
Click on "View connection properties"
Your router should have those same "Security" settings.
When I first started using it, it was working fine till this morning, but suddenly this problem developed. I have not made any changes. When I tried to open my Chrome browser, It shows "sending request", but after some time "Unable to access network", even after repeated trials.
In reply to Mr.Sardonicus suggestions,I have tried all those. Security type is WPA2-personal. Yes I have fed the right password, but no improvement.
OK, one last thought before I go and then I'm going to yield to Mr. Sardonicus because it is tough to work with two people at the same time. Anyway, going back to "it worked fine until this morning", my other thought would be that maybe an update broke it (a non-driver update), so you could consider uninstalling any updates that were applied since the time it last worked. OK, I'm outta here. Good luck.
1) Is the service provider down -- it does sometimes happen - you can check that easy enough - phone the service number (hopefully it's not via 97 zillion menu choices, a 40 minute wait and a totally uncomprehensible voice from the other end of the planet when you finally get an answer).
2) Have you been disconnected -- Bill payer not paid etc or changed service without notifying you. -- this happens sometimes too. !!!
3) ISP connections OK - look at the setup that the ISP requires.
4) Password correct (The ISP one not your Router's admin screen).
Now what sometimes can happen too is that another device such as a mobile phone or music streamer has grabbed an IP address that your computer wants to use and you don't get a message -- so you never get connected to the net. If you've got a smartphone see if you can get a Wifi connection. If you can then switch off ALL the computers in the house, and your phone (Mind you these days most people don't even realize that phones actually have an OFF switch !!) and the router. Wait 10 mins then switch on the Router again, then computers one by one -- ensure the network settings on the computers are to use DHCP and then finally your phone (do the phone LAST).