I hate it when this happens, I have often had the problem where I open my pc for one reason or another and it won't prost when I put it back together, first thing to try is resetting the bios, eiether removing the battery or using the battery short jumper, do it for a few seconds to be sure it resets. If this doesn't help strip the computer down and then put tha cpu, ram and vid card in and nothing else to make sure you can boot, then add each component 1 at a time and hope it works, if it stops after you add a component then that may be dead, if it doesn't post with the bare components then try testing the seperately in another machine. The computer not posting and giving no beeps is usually something to do with ram, the cpu or motherboard, I have no idea why mine refuses to post like this and after reconstructing it it works every time it's just one of those things that happens with such delicate and complex equipment.