Try taking off the bottom screws again, but leaving on the bottom, and try turning it on like that, just to make sure the screws were not causing the issue.
If the device will not turn on at all, as in no fans, no sounds, nothing on the screen, its reasonable to assume something was damaged when you took off the bottom. If the device does turn on to some level, but wont reach the login screen, that is a different story. Could you clarify what happens when you try to turn on the device?