Hello,
I recently got RB751G, so I am newbie;)

RB751G is with RouterOS 5.15 and I have problem that my ethernet between my desktop and router is only 10mbit. I setup autonegation on booth ends and they works at 10mbit only.
I tested this case with my notebook that have gigabit ethernet and it works at 1gbit. I don't change anything, e.g the same configuration and port at router side with the same cable.

I can manually force(autonegation disabled) my desktop and router to 100mbit - this works, but with 1gbit doesn't.
My desktop has integrated, from device manager "NIC nvidia nForce 10/100/1000 Mbps" and motherboard chipset is nViidia nForce 7100-630i.
I previously used other router tp-link TL-WR1043ND and it works with this NIC at 1gbit.

Could you provide any suggestions what is wrong?