i have a laptop and a pc connected to the internet,
if i connect the laptop to the modem through a cable the internet drops occasionaly

if connected through the router is drops a lot, is this the router or modem?

Since the amount of disconnections increases when the router is introduced, it could be both.

But as the modem drops without the router, one would have to start with the modem and reassess the router once the modem connection is secure.

Of course it might not be that the modem is faulty, it could be a line problem. Either internal to your house or external.