For some reason, my computer did not shut down correctly last time, and now when I boot up the system, a DOS-style screen pops up saying "Windows did not shut down successfully..." and prompting me to start it in Safe Mode or start it normally.
Regardless of what I choose, it goes to the "Starting Windows" screen, and shows the Win7 animation, then it shows a black screen with just a mouse cursor I can move around, but nothing after that. Normally it shows the Win7 login screen. Ctrl + Alt + Del does nothing... I've tried powering off the tower entirely and unplugging and then powering back on, but I always get the same Safe Mode prompt, and the same black screen.
On black screen with mouse pointer try pressing ctrl+shift+esc and then click file>run new task. Type in cmd and check 'run as administrator' option.
Finally, type in sfc /scannow and see if it fixes the problem you're having.