What are the Troubleshooting steps you have tried?
Have you tried Microsoft website?
Do you have the Blinking Cursor?
Access the link below and try to perform a starup repair, as it might help us to fix the issue.http://support.microsoft.com/kb/925810
If the issue persists after performing the startup repair, try to perform a system restore.
1. Insert the installation disc.
Note The computer must be configured to start from a CD or from a DVD. For information about how to configure the computer to start from a CD or from a DVD, see the information that came with the computer.
2. Restart the computer. To do this, click Start , click the arrow next to the Lock button, and then click Restart .
Note If you cannot restart the computer by using this method, use the power button to turn off the computer. Then, turn the computer back on.
3. Set your language preference, and then click Next .
Note In most cases, the startup repair process starts automatically, and you do not have the option to select it in the System Recovery Options menu.
4. Click Repair your computer.
5. In the System Recovery Options dialog box, click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options menu, click System Restore.
7. In the System Restore dialog box, click Choose a different restore point, and then click Next.
8. In the list of restore points, click a restore point that was created before you began to experience the issue, and then click Next.
The computer restarts, and the system files and settings are returned to the state that they were in at the time that the restore point was created.
Post back if it is not working we will be happy to help you.
Hope this helps.