We got a Win7 Ultimate SP1 64-bit. I suspect that OS drive (only one C:\) might be damaged because sometimes the machine rebooted itself. Ran diagnostic utility at BIOS. The errors pointed to hard drive or graphics card. Now the graphics card has been replaced.
I wonder if Win 7 provides a way to dump out the whole disk image and can restore back to another new hard drive later. (I would like to replace the hard drive but don't want to reinstall all the software.) Or I have to use some kind of software to clone the C drive.