First, try removing any expansion cards and reseat the entire expansion riser card. Then, try removing the second processor, swapping it with the first processor if still no video.  (Make sure that the processor is unstuck from the heatsink before reseating the processor - use a credit card if it is stuck.)
i got a pe 1850 and it worked fine yesterday booting up normal and loading into windows ent. 03 then this morning i got no video the fans dont spin up real high at first like normal, no beep codes but i got the amber light flashing. the keyboard lights light up once at first then nothing. usb mouse has power. it has 2 costa rica xeons @ 800 mhz and duel psu's 1 gb of ram over 4 slots. i tried to reseat them as well. and even tried to powerup with no ram and i didnt even get the no ram beep code it has 2 147gb 15k rpm hdd's and i dont get any lights on them either. they to worked yesterday. . the beeps worked yesterday i remember. i reseated the raid ram too. i took out the battery for a couple min utes to no avail. i tried with only one psu too.
poweredge 1850 wont post or no video