+1 for WSUS - especially if you have a lot of updates to install. Windows seems to simply fail to work in the case of say 200 updates.
If you are having Windows Update problems it is also worth checking/repairing the Windows files with:-
if unfixable errors are reported then
dism /online /cleanup-image /restorehealth
then repeat sfc /scannow
You need to run the above in an Administrator command window.