I would suggest you to check if the GUI boot is unchecked in system configuration.
To do this, follow these steps:
1. Type msconfig in start search box, press Ok.
2. In the system configuration window, click on Boot tab.
3. Uncheck the option ‘no GUI boot’ if it checked.
4. Click on Apply, OK.
5. Reboot the computer and check.
If it does not help, try to run a System File Checker [SFC] scan on the computer which will replace the missing or corrupt files.
To do this, follow the steps given below:
1. Click the Start button.
2. From the Start Menu, click All programs followed by Accessories.
3. In the Accessories menu, right Click on the Command Prompt option.
4. From the drop down menu that appears, click on the 'Run as administrator' option.
5. If you have the User Account Control (UAC) enabled, you will be asked for authorization prior to the command prompt opening. You may simply need to press the Continue button if you are the administrator or insert the administrator password etc.
6. In the Command Prompt window, type: sfc /scannow and then press Enter.
7. A message will appear stating that 'The system scan will begin'.
8. Be patient because the scan may take some time.
9. If any files require replacing SFC will replace them. You may be asked to insert your Vista DVD for this process to continue.
10. If everything is okay you should, after the scan, see the following message "Windows resource protection did not find any integrity violations".
11. After the scan has completed, close the command prompt window, restart the computer and check.
For further reference check the link given below:
How to repair the operating system and how to restore the operating system configuration to an earlier point in time in Windows Vista