Alright i just got an old e510 and i dropped in a new 500watt psu that works fine and is overkill for this system really. Anyway everything was stock inside until i swapped out the psu. Anyway then i wanted to upgrade from the x600 to a 9800GT. Both these cards worked fine I've repeatedly tested both on different systems. I can remove the x600 and it will boot. But the second I hookup the 9800GT i get that amber light of doom. So i unplugged all peripherals and even took out the tv tuner(no rationale behind that really just desperation) and still the amber light kept mocking me and my incompetence. I swapped out the mobo battery. Though it wouldnt have booted the first time around without the card. Were that the case. I reset the password jumper on the board and basically attempted every know fix for the amber light problem. But if i plug the x600 in it works fine. Put the 9800 in another computer and it works fine. Hoping that somebody out there knows what this insanely annoying problem is.
Despite the power rating of 500W, perhaps Dell designed your PSU to power only the x600? The 9800GT has a significantly higher power requirement, and needs more consistent and clean power delivery; maybe your current PSU provides neither.