No beep, no BIOS screen, full power - What can be wrong with my Dell XPS Gen4

Hello,

I have a DELL XPS/Dimension XPS Gen 4. All diagnostic lights are green (A, B, C, D)
Nvidia 6800 video card.
Pentium 4 Prescott Dt, Pentium 4 Prescott DT, 3.4GHZ, 1 MEGB, 800FSB

It is exhibiting similar behavior as in most other cases listed here (no beep, no video, all fans, drives power up).
Checked CMOS battery. It was around 2.8. Replaced with 3.3 v new battery. No improvement.
Checked monitor - works with another computer. Works with another computer using same video cable.
Other monitor does not work with this DELL XPS either (no signal).

Here are the voltages measured with a multimeter.
PSU plugged in - Not Powered on.

Green Wire 3.37 stable
Grey Wire 0.00
Purple Wire 5.13 stable

Blue Wire 11.87
Orange 0.00-0.01
Red 0.00
White 0.00

Powered up

Green Wire 0.13 stable
Grey Wire 5.12 stable
Purple Wire 5.11 stable

Blue Wire 11.92 (or -11.92)
Orange 3.36
Red 5.12
White 11.86

P5 Connector (for graphics card) 11.82

I did get some beeps when I pulled some memory out of banks (so that there were not matching pair of memory in a bank).

Computer was working fine until about couple of weeks ago. (Used to have some trouble with lockups). running Win XP pro. I have tried other monitors but no luck. Dell no longer makes the power supply for this model and the only thing I can find on ebay are refurbs. So if it is not the power supply, I'd rather not try to get another one. But all fans come on, no leaky caps on MB, lights on motherboard, graphics card fan comes on (I would have thought if the graphics card was bad, I would get some beeps and codes).

I tried getting all the readings Westom had asked for from other users in an older thread.

Any help you can provide is greatly appreciated.

Solved - apparently it is a dead graphics card (Nvidia 6800 GTO)

OK thanks. Fiddly card seating can always be a problem and I use surge protected sockets to try and eliminate spikes and so on.

Ok - Tried it. Removed fans, removed cpu heatsink - cleaned cpu and heatsink - removed all old dried out thermal grease - applied new silver thermal grease - reassembled (had to move heat sink around and attempt rebooting while nudging the heatsink). Eventually had to run a wire loop thru case to apply some pull using a metal post on top of the heatsink to pull the heat sink back towards the back of the case with a little pressure). Computer booted up with no problems. Problem solved.
(Now I will have to see if my old graphics card is still good).
Details were originally posted by vaporize in this thread for an 8400 (similar problem)
http://www.tomshardware.com/forum/ [...] 2_100.html