Sometimes the Windows folder gets loaded up with crap. I just saw a computer where it had ballooned up to 240GB. Try running Disk Cleanup.
- Type "Disk Cleanup" in the start menu. Then select disk cleanup.
- Select your boot drive
- Click the button to clean up system files
- Select your boot drive again
- Check every option within "Files to delete"
- Click OK
Clear up as much space as you can before doing this. I don't think 516MB is enough free space for disk cleanup to work. Move all user files to an external hard drive. Clear the cache on all your browsers. Turn off restore points. Manually set your page file to something like 100MB or better yet switch it to another hard drive disable on C and put on automatic on the other...