wont even turn on at all?? no fan nothing?? what did you put your motherboard on when you cleaned it?? also, did you make sure to dissipate all static from your body by touching the chassis of your case often when removing/replacing the motherboard?? Did you knock your heatsink any?? could be thermal protection.. but in that instance your system would probably boot for a couple of seconds then turn off.. make sure your motherboard power harness is correctly clipped in to your motherboard.. make sure all your pci cards and agp cards are locked in place tightly... make sure your battery isnt loose.. make sure all front panel connectors are correctly in place. try putting one stick of ram in the slot nearest to your CPU. make sure ALL connections are properly made. as a last resort, try resetting your CMOS.. its a long shot but hey. who knows?? good luck, friend.