Ok, If you can login, and nothing comes up, press CTRL-SHIFT-ESC to bring up Task Manager, then click File, New Task (Run...) Then Type the drive of where Windows is Installed (EG: C:\Windows) That should bring you to the Windows Directory.
In there, you need to see if you can find Explorer.exe, if its there then read on other wise skip the next part.
Go back to the Task manager and select new task, Type regedit and hit enter. Then navigate to HKEY_LOCAL_MACHINE > SOFTWARE > Microsoft > Windows NT > Current Version > WinLogon
Then find the the String Value "Shell" Without Quotes. Double click and make sure it says explorer.exe, if it dosent, then change it to Explorer.exe and hit OK.
If the Value isnt there, right click and create a new String Value, Name it Shell, then double click and type explorer.exe
Restart the System.
If Explorer.exe is not present in the Windows Directory, you will need to repair with the Windows 7 DVD. Insert the DVD and restart the system, boot into the DVD and wait for Windows to load files. Then Select your Language and click Next. There you will see Install Windows, Instead, click Repair My Computer (Located Bottom Left)
Let Windows Search for the Installed OS. Then It should automatically Repair. If not, Click on Repair My Computer after the Search for the Windows Operating System is Over.
Hope this Helped!
-sM4llziE