Hi Mary,

I'm assuming here that absolutely nothing comes up on the screen. You don't see the Windows logo. You don't see the manufacturer's logo. You don't see a blinking cursor.

Video adapter problems are the most common cause of this issue.
Try the following troubleshooting procedures, in order. If the steps in the first procedure don't fix the problem, move on to the next procedure.

Reinstall your video driver

1. Right-click the taskbar, and then click Start Task Manager.
2. Click the Processes tab, click explorer.exe, and then click End Process.
3. Click File, and then click New Task (Run).
4. In the Open text box, enter explorer.exe, and then click OK.
5. Click the Start button, enter device manager in the search box, and then, in the search results, click Device Manager.
6. Double-click Display adapters, right-click your display device, click Update Driver Software, and then follow the steps in the wizard that appears.

After the driver is reinstalled, you might need to restart your computer again to complete the installation.

Check for registry issues

1. Right-click the taskbar, and then click Start Task Manager.
2. Click the Processes tab, click explorer.exe, and then click End Process.
3. Click File, and then click New Task (Run)
   In the Open text box, enter explorer.exe, and then click OK.
4. Click the Start button, enter regedit in the search box, and then, in the search results, click regedit.exe.
5. Browse to the following registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
6. Click to select the WinLogon key, and then, in the right pane, click Shell. The value of Shell in the Data column should be explorer.exe. If the value of Shell isn't explorer.exe, double-click Shell, and then, in the Value data text field, enterexplorer.exe, and then click OK.
7. Close the registry editor, and then restart your PC.

Start the computer in safe mode and run System Restore

1. Click the Start button, click the arrow next to Shut Down, and then click Restart.
2. Do one of the following:
   
   • If your computer has a single operating system installed, press and hold the F8 key as your computer restarts. You must press F8 before the Windows logo appears. If the Windows logo appears, try again by waiting until the Windows logon prompt appears, and then shutting down and restarting your computer.
   • If your computer has more than one operating system, use the arrow keys to highlight the operating system you want to start in safe mode, and then press F8.
3. On the Advanced Boot Options screen, use the arrow keys to highlight Safe Mode, and then press Enter.
4. Log on to your computer with a user account that has administrator rights. When your computer is in safe mode, you'll see the words Safe Mode in the corners of your monitor.
5. Click the Start button, type "system restore" in the search box, click System Restore, and then click Next. 
6. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
7. Choose a restore point when your PC worked as expected, click Next, and then click Finish.
8. Restart your computer normally.

If these steps solve the problem, you're done. If not, try repeating the steps and selecting an older restore point (if one is available).

I hope this helps.

Regards,
Lokesh