Hello,
I have trouble to have access into my old RB 133C3 - Winbox Neighbors shows my RB, but I cannot connect with it.
Alert:

Router has been disconnected

I tried to make a hard reset - I put a jumper as in the picture and connected the power supply - the problem is still the same

https://wiki.mikrotik.com/wiki/Manual:Reset


Any idea how to solve it?

You might be using a version of winbox that is to new for the device, if you cant reset it through the pins try connecting to it via the serial cable and either configure it through that to get a internet connectivity and upgrade the device or set it to system>routerboard try ethernet once then nand and try and netinstall the device to a newer version of router os.

This one only supports RouterOS v5, so use old Netinstall and old RouterOS for this one.