You can log on at Microsoft's update page and it will check your computer for MS updates it needs. You can also, from that same page, ask for a summary of all of the updates you have downloaded and installed so far--take a look for it there; if it failed, it should tell you. You may have to redo the installation, and it should write over any files incompletely downloaded or installed. If you don't like SP3, then you should be able to uninstall it. Right now you're in limbo, the only thing is to move forward and install it and work from there.