This article explains how to start Windows 7 and Windows Vista using the Last Known Good Configuration (LKGC), provided that Windows was functioning correctly before the last time it was shut down.
Windows 7 – Use Last Known Good Configuration
Press the F8 key repeatedly as soon as, or just before, the Windows 7 splash screen loads (i.e., continue holding the key as Windows starts). This will load the Advanced Boot Options menu.
Use the arrow keys on your keyboard to highlight Last Known Good Configuration (Advanced), and then press Enter.
Wait for Windows 7 to boot, hopefully normally. It shouldn't take much longer than you're used to.
