Windows won't start normally

Suddenly, Windows7 won't start and I can't figure out the cause.

Symptoms:

- System boots, it reaches the welcome screen where message "Please wait" is displayed.

- After a few tens of seconds the screen turns black

- After a few tens of seconds with the black screen, it goes back to the welcome screen displaying same message, and then it goes to the black screen again.

This cycle repeats maybe 10 times or more, then it reboots, and when the welcome screen is reached, the following message is displayed:

"The System Event Notification Service failed the logon.

The remote procedure call failed and did not execute."

I unplugged all peripherals and USB devices, including printer and mouse and tried again, but same result.

But in Safe Mode, it starts without problems.

Where should I look to figure out the problem..?