Inspiron 5100 shuts off after 10 seconds, caps lock and scroll lock solid

i tried removing each of the components, one by one: optical drive, hard drive, battery, RAM (not necessarily that order). i thought i would try removing the system battery too but, after stripping down the system, i found that it was soldered to the mother board. the CPU thermal compound looked a bit thin/worn, so i cleaned it off and replaced it. i also trying pushing Fn down while powering up. i never get any video, no dell logo or anything on screen... the backlight doesn't even light up. any idea what the problem could be? i can't seem to find any documentation on the keyboard lights... thanks