Lenovo laptop not picking up Wi-Fi?

It only worked when I plugged in an enthernet cable. But for the past days I've been getting "no Internet connection", when I plugged it in. Then few minutes later its back to "connected to internet" then "no Internet connection" again. And my internet/router is not the problem.

If this is happening with a wired connection this is unusual, and would suggest a router problem check the cable or try a new one
Make sure the Wi-Fi is switched on, can other devices access the router? If you want further help update your post with model of levono and your operating system.
When you try to access the Wi-Fi is it picking up any other networks? Have you tried the network troubleshooter?
May be the simplest thing would be to buy a cheap USB Wi-Fi adapter such as this rather than fiddling about
http://www.cclonline.com/product/39853/TL-WN821N/Wireless-Adapters/TP-Link-300Mbps-Wireless-N-USB-Adapter/NET1194/

Look at your firewall and AV settings to see if there's anything there which might be causing the problem. Next look at the Internet Options. Check and see if there are any proxy settings. Check for malware, particularly browser hijackers (use Malwarebytes Free edition and/or SuperAntiSpyware, Adaware, Spybot Search & Destroy, ADwcleaner).

My lenovo s850 is not picking my Wi-Fi router signal but is picking other neighbourhood routers? What can be possible problems?