SP2 has been replaced by SP3, which should readily download thru Microsoft Download.

If you cannot get SP3 via Windows Update, go here and download it to a folder of choice on your hard drive that is easy to find later.

 

http://www.microsoft.com/downloads/details.aspx?FamilyId=5B33B5A8-5E76-401F-BE08-1E1555D4F3D4&displaylang=en

 

Reboot into safe mode and execute the file you just downloaded to install SP3

 

Safe mode, restart the PC, when you see the Dell logo, start tapping F8 to get the windows advanced screen, then choose "safe mode" hit enter key, let it load into safe mode, it will look strange, click yes to confirm safe mode, when you get to your strange looking desktop, find that file you downloaded and execute it, follow the prompts, when its done (takes a while be patient) restart the PC (don't use F8).

 

Now do a Windows update to get any recent updates that are available.