urgent

[kwokwai]

I received an urgent call from a friend. He said his Windows (XP SP1) was just staying at the Welcome Screen. He complained about it to me that he has waited for more than half an hour, but he just couldn't get into the DeskTop.
I went to help him, just a twenty-minute walk.

Ok, what I had tired were as follows:
1: Turn the PC on, and the PC really just stayed at the Welcome Screen. We both waited for more than ten minutes.
2: Try to go into Safe Mode, but the system just restarted itself instead of showing me the safe mode DeskTop Screen.

3: Put the Windows CD into the CD-ROM. I tried to reinstall the Windows for him. His HDD has got 40GB space totally, with 3 partitions
(D: 20GB for Windows; E: 10GB for HomeWork, F: 10GB for other files).
When the Windows CD had already loaded, there were several options:
1: Add Partition; 2: Delete Partition;
3: Install Windows into the selected Partition
but, why there is no the fourth option for formatting the partiton?

I tried to install the Windows in partition D, but it just warned me that partition D has WindowsXP installed already, and said if I tired to install the new Windows into partition D, the system may not be stabile...

Oh... I was lost... I don't know what I should do for him!

Please help!