Hp proliant microserver hardware failure

I've tried starting up my micro server, I think it's the proliant n40l but not positive there's a serial number but can't find the model, it's been sat around not doing anything for a while when I've tried starting it up the hp symbol on the front of the machine stays red and I can't get into bios, I've pulled the tray out and reseated the ram with no luck, I've also pulled out the added graphics card and all the hard drives.
I'll check when I get home if it'll start with 1 stick of ram at a time, if that doesn't work I'm thinking this only leaves either cpu or motherboard?

Is there any way of figuring out which one it's is without having to replace each one?

Would a dead button battery stop the machine from starting or is there anything else I'm missing that I could try?

Thanks

I'm not sure what model proliant it is so can't get the manual but there aren't any leds on the mobo anyway,
With you on the button battery but after another hour of messing I finally found a battery swapped it out and it started up!
Wheres the face plant emoji!


Thanks for the help

Faceplant for not trying the easiest thing first but yes deffo thumbs up that it's working, I'm On my mobile how do I mark it as solved?