Hi @mrads_
Either the battery is missing, dead or there's a motherboard problem.
You could try a power refresh to reset the BIOS and check what that does.
Disconnect the charger (if connected), remove the main battery (if it is there) and then open the laptop and remove the coin cell battery from the motherboard.
Go to p.17 (of 56 pdf) of theowner manual to view the procedure to remove the coin cell battery.
When it is out, measure its voltage. If it is <2.5V DC or if the battery is >4-5 years old, replace it. The battery type can be found on the battery itself. Usually it is a CR2032 which is available most everywhere e.g. supermarkets.
Press and hold the laptop's Power button for a full 30 seconds and then release it.
Reinsert the coin cell battery (or replacement coin cell battery) onto the motherboard, reassemble the laptop, insert the main battery, connect the charger and check.
Best that I can find is that the laptop supports a maximum of 8GB of DDR2 6400 800MHz sodimm ram over 2 slots i.e. 2 x 4GB
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