I just replaced some parts in my dad's old computer. I gave him a new us, new video card, upgraded the RAM, etc. While I was doing that, I decided to repalce his old Sempron single core processor (which I saw was AM2) with an AM2+ Phenom X3 8550 Triple Core. When I installed it, nothing happened. The computer was running (fans etc) but nothing appeared on the screen and the blue led to let you know the computer was on was not on. I then put the old Sempron back in and BOOM it started just fine. What am I doing wrong? I've built many computers before and always thought AM2+ would work in AM2. Thanks TPU.