My web site had not been Responsive

Could you help us by adding more information? Do you mean that the site design no longer responds to different screen sizes correctly or do you mean that the site is down? If down, what error messages are being displayed, etc. Thanks in advance…

the site is not down, but in mobile and tablet the side bar disappear and some distortion in width.
It was working good a few days ago, before upgrading worpress

Right, that’s very helpful. Thanks.

Typically, responsive issues are theme/CSS/template driven. There is also some code that drives layout within plugins. We need to find the code that isn’t up to snuff. Could you please check the following:

1. Disable all plugins to see if this fixes the problem. Then load them one at a time. This will tell you if a single plugin is conflicting with core.
2. Update your theme by contacting the people who created it. Often theme developers test and release a new version when core is updated. This is the most likely culprit.

I hope that this is helpful in return.

I did, but without all plugins and also after adding one by one,nothing changed, also not responsive !!!
Kindly help me,
Also pls let me know how can I re install wordpress 4.2.1 to fix that??
Can I cancel any updates in the future to avoid that??

The problem you’re describing isn’t a problem with WordPress. It’s the other way around. Disabling updates is not a good idea for several reasons. The leading one being security. Updates going forward are automatic and will happen in the background so let’s focus in a different direction. the better solution is to work with the theme developers. What theme are you using?