I'm not sure what make and model you have but when the system boots up and after the BIOS has done its checks, start pressing the F8 key gently once a second before Windows begins to load.
This should display a whole list of Safe Mode options.
The top one is Safe Mode itself. If it is not highlighted, use the keyboard arrow keys to select it, then press Enter on the keyboard. Hopefully this will load Windows 7 in its diagnostic mode.
See if it loads into Windows. The display will look very different because only generic drivers are loaded. if that works, reboot and it should attempt to load back into Normal Mode.
If that fails, either Windows does not load into Safe Mode or when it does and you reboot it still fails to load properly, reboot again into the Safe Mode list of options, select the top choice again, then try and access Windows "System Restore" from the Start menu bubble. You will need to log in as an Administrator for this to work.
If all that fails, there is another option in the Safe Mode list of options, "Last known good configuration, (Advanced)".
Try that. This will attempt to load Windows from the last back up registry. Again, you will need to log in as an Administrator for that to work.
Let us know how you get on.
Yesterday my computer was okay, then my AVG program popped up and said I had a virus. I closed all my other windows then did disc cleanup and defrag (I know this probably has nothing to do with viruses--but I don't know--I just did it to be safe) and I opened up my AVG. I checked for updates then looked at the viruses again... I just clicked "Remove all unhealed infections" and a window came up telling me the virus vault is full, and asked me if I was sure I wanted to delete the files. I just clicked yes. I scanned my computer again and I thought everything was okay, I restarted it. Then it will give me the loading screen and say it's configuring the data, but it won't go to where I sign into my account. It just stays a blank gray screen. I don't know how much any of this has to do with my problem, or why it's happening or how to fix it. Also, I have Windows 7. I would really appreciate some assistance! On another note I'm 15, and technology isn't my best area. Thanks for reading this.