I had the same problem with mine, i tried the thing guitarfish suggested but that didn't work. Didn't understand how it can be becuase of the date and time, after hours of searching on the net, I managed to fix the problem myself and heres how i did it
click on your time and date (bottom right) then a windows should pop up, click on the link 'change date and time settings'. on the date and time window click on the internet time tab, click on Change settings button, then click on the 'update now' button, then click ok and exit the windows and now try your update.
it should work as it did for me
good luck