Windows 10 build

Just downloaded what is supposed to be latest build for windows 10 and now nothing works,how do I get my computer back please.

You'll have to provide us with a little bit more information such as what error are you getting when you boot your computer? The most generic answer would be to boot your computer from a Windows 10 install USB/DVD, select the language and keyboard, then on the next screen click "repair this computer" option - then troubleshoot - then advanced options - then restore previous version (or build, can't remember which).

Unable to operate machine as it will only go as far as starting up and goes no further.

This trouble started when I went into download updates and I was offered to update to so called latest build.Like a fool I accepted the offer and now when I power up all I see is the W10 small window figure with the light shining through,my name and then a small broken circle going around.Hope this helps.