Windows 7: Black screen on startup, showing cursor, doesn't go to log in screen.

I'm using I have a DELL4500S desktop, on startup it will not go to the login screen, the screen is just black with the cursor showing. I've tried restarting the computer, unplugging everything and restarting it. Nothing is working. When it first starts a pop up shows and says

"This Application has failed to start because SAMLIB.dll was not found. Re-installing the application may fix the problem."

I'm not sure what it's talking about and what to re install and I can't reinstall whatever it is because I can't get to the start menu.

Help? I don't know what to do :[

SAMLIB.dll is a security account manager dynamic linked lib. A repair install from the dvd should fix the problem unless you are infected with malware, or have a modified system

Not sure which disk to use that I have
"Application (for installing/reinstalling roxio easy CD creator 5.2 basic)"
"Drivers & Utilities (Dell dimension resource CD for reinstalling device drivers and using diagnostics, utilities, and online documentation)"
"Display by Dell (E772c Color Monitor Quick Setup)"
"Application" (Dell tools CD for reinstalling dell-installed software)
"Drivers & Utilities" (For reinstalling conexant 56K data/fax modem software for microsoft windows)
"Microsoft"

Doesnt appear you have either a win 7dvd or a restore dvd. You may have to do a reset to factory settings, you should read the owners manual and look in our tutorial sections for instructions on how to do that.

The reset will require re-installing your apps.