While at the black screen with cursor, Press CTL, Alt, Del and choose to bring up
Task Manager. Look for the process "explorer.exe" and highlite and then end this task. Then while in Task Manager, click on File - at the top and choose "New Task". In the Open box type "explorer" without the quotes.
If that fails, try:
1. Boot from the Windows 7 install disk
2. After choosing your language, choose the "Repair your computer" option on the "install now" screen
3. Optional step: if you need special drivers to access your hard drives (SCSI, etc), follow the "load drivers" onscreen instructions to read them from an external source.
4. When prompted, choose the "System restore" option
5. Choose one of the previous restore points (I chose the second one down on mine just to be sure)
6. The system will roll back installs to that restore point; reboot only when prompted
If both fail, read here for more info:http://support.microsoft.com/kb/314503