Win 7 black screen defies resolution... here's what I have tried...

Client called saying she turned her PC on this morning and it booted to a black screen with functioning white mouse cursor.
I found that safe mode with networking provided a normal display, so I first suspected a driver problem.

1. Checked the registry for errors in hklm/software/microsoft/windows nt/winlogon and confirmed that the shell=explorer.exe and userinit=c:\windows\system32\userinit.exe, (including the trailing comma) were correct.
2. Ran a complete malware scan using bitdefender (from CD off-line boot) and malwarebytes from within windows. Nothing found except for an on-line shopping BHO that I uninstalled.
3. Tried another monitor since this was a Samsung auto-sensing monitor with multiple inputs.
4. I uninstalled the Intel HD video driver. Rebooted in normal mode and found that the VGA driver would work just fine. To me this just reaffirmed that it was likely a driver issue.
5. I reinstalled the Intel driver from the Intel website. The black screen returned.
6. Ran system restore from a restore point 4 days old, before the problem existed. The problem remains.
7. I reinstalled windows from an image that was a little over a week old. The problem remains.
8. I finally gave up and tried to make her VGA display as palatable as possible with the promise to return as soon as I could figure out a solution.

Any and all ideas would be appreciated.

Thanks Andrew. I hadn't even thought about bad RAM. The video is on-board so I thought I may end up installing an external card, but it may make sense that a portion of RAM is going bad. I do not know if this particular Lenovo PC uses shared memory with the CPU or not. Since it's on-board it may. I will take a PCIe video card with me but also run MemTest86 on that bad boy first. Thanks !