Please perform a Clean Boot (this will ensure no 3rd party application is interferring with the installation) and step through the steps below:

1. Since you already downloaded and installed theSystem Update Readiness Tool, please just run the tool again and take note of the errors.

2. Click Start type cmd (you should see the command prompt populate at the top) Right-click it and select Run as Administrator
Inside the prompt type sfc /scannow

*For more information regarding theSystem File Checker.

*If corruption is found, seeHow to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7.

3. Once the SFC is complete,Check your hard drive for errors.

4. Run the System Update Readiness Tool again. If the errors have been cleared, try installing Service Pack 1 again. If not, move to step 5.

5. Perform aStartup Repair, upon startup, try installing the Service Pack.