HP n5420 won't boot

I have an old n5420 HP laptop that I want to use but it won't boot up. It worked fine and just quit a couple of years ago.

When I power it on it is showing that the AC adapter is working (green light is on) and I hear the fan (CPU fan I think) spool up. Nothing happens on the screen and then the fan shuts down.

I have tried to re-seat the ram per HP's website and also made sure there wasn't any media in the drives.

I hooked up my regular monitor to it to make sure the monitor wasn't the cause as well.

There are no 'beeps' to make me think it is software. Is there anything else I can do?

When this was new it cost $1200 so I don't want to just trash it.

Please help!

 

Have you ever replaced the coin battery?

 

I don't know how to get to it. The only thing I can get to easily is the RAM and another spot. (video card possibly?)

I tried to take it apart to no avail... I don't want to ruin it to get it apart and just never really had the time to figure it out. Seems like I am missing some screws or something.