I have Dell inspiron 6400 alias E1505. I haven't used it for about a month or so. Now, when i am trying to start up the machine, it wont turn on. When I press power button, RED LED flashes just once (battery and AC adapter attached). LED stays on as long as I press power button.
I think the problem that you have is related to the hard drive. Since you said that the laptop doesn't turn on probably the failure of the disk is mechanical and you might consider of replacement of the drive.
To be sure that's the reason for your laptop not to work I suggest you to test it on another PC via SATA-USB cable if you have one. If the hard drive does not spin at all being connected to other ports, then it's gone.
You could also try the RAM stick on another laptop to see whether it will work there.