The Reg Model is D05S
Recently it has been performing really slow, taking hours to apply windows updates, etc. (please no windows jokes) ;-)
After a reboot, the POST screen came up but then it stopped, shutdown and power cycled again. This time it was in a power up, no post screen, shut down, power up, no post screen, rinse, repeat loop. The power up showed power button light, panel lights and fans spinning up. NO BEEPS. A recent Dell Quick Diag in the OS showed everything was ok.
Unplugged everything, still no love.
Opened the case and cleaned all the dust, still no love.
Looking at the posts in the forum, most lead to dead links.
link to article about dead computers is not valid.
then the FAQ link to No post troubleshooting is dead
Looking around, there was two suggestions that seem to be my guess too, bad internal power board or power button.
Any suggestions to properly troubleshoot the problem will be greatly appreciated.
It seems like I am in between a No Power and No POST issue.
These procedures are only for users with advanced technical skills ... you have been warned.
With x51's laptop-like power system, you can't really fully use a convention desktop Digital Power-Supply Tester. However, it might sorta-work since there might be some standard power-connectors inside.
Test AC Adapter for proper voltage output with volt-meter. Doesn't mean much since there is no load on Power-Supply, but it's a start.
With machine open (and nothing shorting-out or touching). Connect AC-Adapter. Test AC-Adapter's output at the Power-Board's Input side. This is really the only way to test AC-Adapter under-load (where it counts). If good, continue.
Test for all primary voltages on Power-Board's output side. They should be similar to a conventional desktop Power-Supply (12v, 5v, etc.).
Power Switch works like any other computer. It's either closed always or momentary closed/short.
While trouble-shooting basics, try not to get to hung-up on the idea that this is special or Alienware computer. However, be sure to get any PDF manuals.
I think x51 might have on-board video (yet usually deactivated). If so, machine should run without dedicated video-card installed.
Thanks for the heads-up. I'll try to check the links in that other post when I get a chance.
Just so you know, Dell is constantly changing their website. Links break and I can't always find the new page URLs. Sometimes, the Articles are just gone.
There is also Google  (seems to index dell.com and forums fairly).
Thanks for the power troubleshooting suggestions but I started troubleshooting with the assumption there was nothing wrong with the power.
pulled components one by one with the same results.
got to the RAM and pulled both sticks. Machine powered and then gave two beeps, no RAM installed.
Installed one stick and it POSTED and shown that the memory amount has changed.
Powered down and swapped sticks. Powered and stayed powered but no post screen.
Swapped sticks back and the power cycling came back !!
I have some DDR3 sticks at work and tried one in DIMM1, posted and booted. Installed second DIMM into DIMM2, powered but no post. Removed DIMM in DIMM2 and the power cycling came back!! swapped for the stick that was in DIMM2, powered but no post.
Removed both sticks and left unplugged for a while. Reinstalled the original stick that worked from work in DIMM1, power cycling. Moved this stick to DIMM2, posted and booted to OS.
This looks like a MB or CPU issue to me. Ideas??
Remember there is also (outside of Windows) Dell-Diags/ePSA. On your way in there each time, check that RAM correctly shows in BIOS.
You are welcome to try each DIMM individually, and each slot. However, if it can't handle a pair of DIMMs, yes ... I would say motherboard or DIMMs. Or, even PowerSupply ... seen it before.
ePSA diag did not show any problems if I was able to get into POST.
I was only able to luckily get back in by swapping the memory or using on a single stick, etc.
Power measurements checked out ok.
Acquired a MB off ebay, swapped it out and now it is running fine.
Thanks for all the help.