I still think Calibre is a great program its just that I cannot get it to work with W10 and my kindle. I suspect there is a setting somewhere which I may inadvertently have changed which has caused the problem.
At this stage I now use the following work around and must admit find it quite a lot friendlier to use. I have downloaded Send to Kindle
http://www.amazon.com/gp/sendtokindle/pc. All I have to do is right click on mobi ebooks that is saved to my hard drive and select Send to Kindle, this then sends the book to my kindle email address or any kindle email address that you have loaded into the Send to Kindle program.
The ebook automatically loads onto my kindle for which you must have your kindle connect to wifi and have a kindle email address which you can set up in Amazon. It does require the ebooks to be in mobi format.
I have also downloaded an epub converter to convert epub to mobi if required. I have found this solution best suits my need in the meantime.
Hope this may help others who may have the same problem and thanks for those that helped me earlier on, it is appreciated.