Black Screen after Windows 7 starts

I started my PC this morning and it went to a black screen.
It boots up normally, BIOS and POST are both fine, the Win 7 logo screen appears as it is starting, then goes to a black screen. No blinking cursor, no mouse pointer, nothing. Ctrl+Alt+Del does nothing. My computer should boot in to the login screen.
The monitor is still on (seen by the blue status light) meaning it is getting a signal.
When I restart I get 'Startup Repair', which runs and fixes nothing. I also tried System Restore to a point from a few days ago, still nothing.
I haven't installed anything new in weeks.
Any ideas?

Right now I am running the Windows Memory Diagnostics Tool, I will post back the results shortly.

My PC is:
OS: Windows 7 x64
CPU: AMD Phenom Quad Core 2300mHz
RAM: 6GB
Graphics: ATI Radeon 5450
MB: Asus M4A78 Pro

try kaspersky rescue disc, you boot it before the O/S starts up and let it run see what results you get I'm betting a corrupt file or some kind of infection. Also you didn't state where or what you were doing before this happened that also does help..............gettingthere

Thanks for the reply.
I am not able to burn a CD right now (I'm on an EeePC), but I will be able to tomorrow.
I did find out that AVG has a command line scan, so I am trying to run that now.
I opened a command prompt from the System Recovery Options. I need to get to my AVG root folder.
I tried to chdir to C:\, but it sends me to x:\. when I try to dir from there I can see that it is not my root drive that win7 is on (theres only about 4 folders in there). I only have one HDD and no extra partitions, so I am guessing X:\ is for system recovery?
Can I not access my c:\ while I am in System Recovery Options?

Now I am running AVG from safe mode. I will post back results.

"...state where or what you were doing before this happened..."
I had just finished playing a game, listening to music and watching a movie. Nothing new, they weren't new downloads. I then shut my PC down for the evening, and noticed the problem when I rebooted in the morning.

AVG did not find any problems.

I am having exactly the same problem within one day with two different Win7 64 Dell Inspirons in two different buildings - both less than 6 months old. Booted up, got "Starting Windows" screen, screen goes black, cursor there and moves, but nothing works. Will not boot in safe mode. Windows repair says that it can't find anything wrong. Got one brief flash message that there was something with a plug and play device driver, but could never duplicate it. Dell and Windows System diagnostics all passed. I was able to fix one using an old system restore point (from a month ago).

The other is a mystery. I only get 3 restore points and none work. Makes no sense, as this is the older of the two computers. I had a huge list of restore points on the other. System restore was not switched off (by me).

Went on with Linux and pulled off the files I need (Fedora 11 Live will mount a Dell/Windows drive - no permission issues). I have some software, though, that I can't really replace.

Was this a bad update......mmmmmmmm.......or is there something else out there. Looking for some direction.