Sadly Greg has provided an accurate summary.
Yesterday our aging ML350 showed an amber light on the front. Taking the side cover off revealed an amber light on the motherboard beside one of the memory modules. Everything seemed to be going nicely. I got my tech to power the system down at the end of the day, earth himself to the chassis and remove all the memory. Then I got him to use the compressed air can and blow out all the dust. Next is the bit that never ceases to amaze me and breaks every warranty rule, every guideline - simply run your finger along the gold memory contacts (both sides) of each module. I'm certain that this acts to discharge static build up (and in our dry air we get lots of that). Put it all back together and turn the power on. No amber lights- just nice green ones where they should be.