|Press Ctrl + Alt + Del to unlock this computer. |
OR try this....
1. Use the Shutdown tool in the Microsoft Windows Resource Kit and attempt to shut down the locked computer. The System Shutdown dialog box is displayed on the locked computer, but the computer does not restart.
2. When the shutdown timer expires, the Welcome to Windows dialog box is displayed.
3. Before the screen saver becomes active, press CTRL+ALT+DELETE, and log on normally.
For more help try here