I have recently gotten a CPU and RAM upgrade for my HP Pavillion G6. After plugging everything back in all that seems to relieve power is the diskdrive, it opens just fine.
Did you put everything back together correctly? Have you tried putting the old components back into it to check for compatibility issues? Did you reconnect the LVDS cable to the screen?
Double check your work and troubleshoot the issue to narrow it down.
If nothing else works, sounds like you might have bricked it.