[Kate2399]

Not sure where you downloaded this SP3, but it hasnt officially been released from Microsoft. You always take a risk of messing your computer by installing unauthorized software on it. Try the following:

when your computer is booting up, hold down the F8 key...when windows tries to start, you will get a screen that now shows..

start windows in safe mode,
start windows in last known good configuration,
start windows normally
and a few other options


Try the one where is says start windows with last known good configuration. NOW, windows SHOULD start properly.
When you close windows after that, and try to restart it, it should be fine. However, if not, you at least should be able to pick SOME option on the F8 screen to at least get into your system, do a backup of important information , and then after doing that, try to reload windows again. When trying to reinstall windows, try the repair option first.