Was SP1 installed on your system before?
There is no good reason not to keep Windows 7 up to date, there is always added functionality and they are not going to document every change in an update, just the majors.
I would suggest installing SP1. Note: SP1 is a major upgrade and should be installed with focus. And always alone (not with any other update).
- Perform a Disk Cleanup and a Defrag beforehand.
- Temporarily suspend any Antivirus software.
- Start the installation and then leave the PC alone. Push your chair back so you cannot reach the desk, go make lunch, anything. Don't multitask.
- When Windows restarts after the install, continue to leave the PC alone. Wait until the hard drive slows down and nearly stops writing. This can take up to 15 Minutes.
Check to see if you can see all of your drive afterward.