What still works is:

• Mac Pro starts to boot
• gives the chime
• Apple logo,
• spinning wheel
• blue/gray screen
• HDD seems to do some more but the screen stays blue/gray.

Thats it.

In save mode it does boot completely.

Please advice in which steps to take to find the cause of this problem.

Extra info:

Mac Pro

2.66GHZ Xeon quad core.

2x512MB RAM

2x1GB RAM

250GB HDD in bay 1 (OSX 10.5.8)

250GB HDD in bay 3 (data)