XP question - Safe Mode vs Diagnostic Startup

[ticker]

What is the difference between booting up XP in Safe Mode and Diagnostic Startup?

My PC has started to spontaneously reboot after ~ 5 mins, followed by an endless cycle of rebooting before it reaches the logon stage. I can boot into Safe Mode and it works fine but if I use msconfig to set it to Diagnostic Startup - i.e. only essential services loaded, I get the same problem.

What is happening in Diagnostic mode which is not happening in Safe Mode. If I know that maybe I can find the problem.

[mittu]

From Microsoft.com :

Diagnostic Startup Starts Windows XP Professional in safe mode with only basic device drivers and services active.

So it sounds as though some device driver is the likely cause of the problem.

[mittu]

Apologies for the double post but this piece of advice may be useful to you, taken from PC Today

The Diagnostic Startup gives you the chance to interact with Windows as it runs through the startup routine. If you run into a problem, the Diagnostic Startup will tell you the name and location of the file that caused it.

The Selective Startup, on the other hand, lets you figure out for yourself the exact cause of your PC problem. To use the Selective Startup most effectively, you need to deselect just one of the files or groups listed beneath it and reboot your computer. If the computer starts and runs without a hitch, you should return to System Configuration Utility and deselect another file or group from the startup routine. Repeat the process until you’ve fingered the file or group that appears to be responsible for your woes. The next step is to open the page that corresponds to the offending file or group and do the same thing—deselect an item from the list, reboot the computer, and repeat—until you pinpoint a particular command or program as the source of trouble.

[ticker]

I used msconfig to stop all services except those which run under Safe Mode. I also tried disabling SYSTEM.INI and WIN.INI. i.e. I tried to get it to boot in Normal Mode in as close a state as possible to Safe Mode. There is practically nothing left. Still the darn thing wont work. I want to know what the difference is between Safe Mode and Normal Startup with everything off.