You should check the cpu temperature in your bios by pressing F12 when your computer turns on.  Perhaps your heatsink needs to be reseated on the processor or needs the thermal paste redone due to not making good enough contact and overheating.

Diagnostics is a good idea.   F12 - boot to utility partition - run the full set of tests

Have you also tried disabling automatic restart?  Didn't specify the OS, but in XP it's Control Panel - System - Advanced tab - Startup and Recovery settings - uncheck Automatic Restart.  Vista should be similar.     Then at least you'll get a blue screen with an error code - and if you're lucky, it's a associated with a particular file name and/or driver.

Another thing to try - boot to safe mode (F8 at boot screen).   If it's stable there,  could be a video issue - safe mode only loads bare minimum default video.

I went through that with a XPS 410 about 10 months ago. Dell put everything in it new and the tech never even got out of the drive way and it was doing it again. They never did get it fixed. They replaced it with a Studio XPS 435 and it worked for about 11 months and it started doing the samething.Dell came out and put a new PSU and new memory and again they haven't been gone ten minutes and the samething. They came back out and put a mb and another heat sink fan and it has been about a month and it is still working. I really believe it's a heat problem or a software problem.The last time it done it was on Microsoft updates. What I done is I kept restoring it back on system restore until it stayed on. It's still working as of right now. 

Everything looks OK.  I don't think its a video issue because the whole system actually shuts down, rather than loss of image and then a system crash.  The computer literally shuts down as it would during a normal shutdown. I'm currently trying to do a System Restore and update my bios and see if that works.  All the actual hardware seems to be working fine.  One solution that I found on another forum post was a faulty power switch (part number is J8995).   Apparently a "fix" is to disconnect the front panel assembly from MOBO.  This doesn't seem like a fix so much as a diagnostic but its worth a shot.  I'll give that a try and see if that works.  I'll post my results. 

I'm running Windows 7 (32bit) BTW.

Thanks for everybody's thoughts!

So,  as a follow up. 

I took a suggestion and ran a system restore.  This seemed to fix the problem, and it has been running well for a month.  No problems.  Until last night.  Windows 7 began downloading an update, the computer was running very very slowly, and after about 30minutes, it shutdown and began trying to restart continuously until I unplugged it.  Never got to the point of booting windows.   Just ran through the drive/ram checks and then shutdown/restart again.  BTW, the power light flashed green/amber.

Anyway, I'm going to try and get it into windows tonight, and do another system restore to see if that fixes the issue.  

Two general questions:

I wonder if anybody has also experienced this after a windows 7 updates?

Also does this sound like it could be a symptom of a hard drive failure?

Hi I have the same problem since May 2010 and finally I got a fix for it.

I must say to solve the problem I changed  the power supply, fan, put fresh thermal grease, switched video card and memory modules. But still no luck. Finally I saw the post by this smart user at http://forums.techguy.org/hardware/818967-dell-xps-410-shutdown-startup.html where he sugeested unplugging the ribbon connector for the power button/audio/usb panel in the front of the cpu.

It works for me..........it is such a simple solution no I think of it. Only a defective power button can cause this problem if there is nothing wrong with you CPU fan/heat sink. I am trying to order the replacement part on Dell but no success yet.

Note this problem has happened to at least 5-6 user this year alone.

Let me know if this fixes the problem for you

Good luck

BTW - J8995 is the part number for the front bezel assembly (with power BUTTON - NOT THE SWITCH) - I know as I ordered one and it's not the part you want. Also, (from another forum) - before trying anything else, try replacing the MOBO battery - it's solved the problem for more than one person. (off to give this one a try)

I am not having the same problem, but I am having a problem with my 410. Basically the monitor will blink within a few minutes after starting the computer and most of the graphics on the screen will freeze. I have tried a different monitor so with the same result so I assume it is a problem with the graphics card. I plan to take the card out and clean the contacts and reseat the card. I am open to any other suggestions.