I'm attempting to install an ATI Radeon 1600X Pro w 512MB into a Dell Demension 4550. The machine is not able to complete POST and I have no video at all. At first I thought the 250 watt PS was not adequate and replaced it with a 500 watt PS. Same problem, still not able to complete POSTand get the famous 3 green and 1 yellow LED's displayed on back of computer and no BIOS beep codes. Reinsert the old video card and I get a message stating Boot did not complete last attempt, check point Vcls failed. Computer then boots up fully with good video.
Dell and ATI not much help except ATI said they would investage sometime in the next 10 months maybe. Dell said to stay with old video card.