To get to the DNA analyzer machine, here are the directions starting from outside the lab (since that'd probably be the easiest way to explain).
Go in the right door (the left is the room where the PC is)
Go straight to the elevator and go down it.
Walk down and keep walking as far down as you can. Then turn left and up and go down the elevator.
Go right, then up, and then to the right again. There should be two elevators next to each other. Choose the one to the right.
This should take you to a small room with the DNA analyzer machine.
(The other elevator-or that left one) takes you to the hallway leading to the keypad.
Hopefully I've got the directions right.