Gateway Startup repair

I purchased my mother a Gateway DX4860 a year ago. It is running Windows 7 Home Premium. It has been doing fine up until a month ago. It started going into startup repair, and saying that it could not repair it. So I did a system recovery back to factory. It worked for 1 week, then did the same thing. I tried system restore again, and it worked fine for a few days. I thought maybe the image was corrupt, so I downloaded Windows 7 from the Microsoft site and installed it using her code. Installed the drivers from the Gateway website. Everything seemed to work fine. I ran all windows updates and installed a fresh copy of Norton. Two days after I give it back to her, she says that it was installing 94 updates and that there was no antivirus, and upon reboot is was giving her the startup repair mess again. I've run Memtest86 and found no problems. Any ideas? I'm out of ideas short of replacing the motherboard or hard drive on a PC that is only a year old.