I have the exact problem as of tonight with my son's hp pavilion 7920. He bought a 256mb dimm of sdram, which appears to be the correct type; he first installed it next to the existing memory, powered up to nothing. I have been working on it all evening; took the battery out, let it sit 30 minutes or so, replaced the original memory and removed the new one, same results. I am stuck, don't want to take it into some rip-off shop like others have. Has anyone found a solution yet? It must be the RAM, since it was working fine right up until the point where he installed it.