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Cisco 891 Router - Black screen when connecting via console

I'm a bit new to Cisco gear. I've inherited a network which no one in the office seems to know the exact structure, so I'm discovering compoments\componets' purpose on the go.
Among these components, I've discovered a Cisco 891 router that's used to direct calls from the VoIP server to a separate internet line from the rest of the data.
I need to modify some rules in the router, but I never got any passwords to it. So, I figured, I'll try connecting through the console port, and try to punch in the default user\password.

I got stuck at the part where I connect to the console.
I'm connected to the router this way:
PC > USB\Serial Adapter > Serial\RJ45 Adapter > Rollover network cable > Router.

After setting the USB adapter to use COM1 as the serial port, and configuring PuTTY to these parameters, I tried connecting:
Speed (baud): 9600
Data bits: 8
Stop bits: 1
No parity
No flow control
I also made sure that in the device's properties, the USB\Serial adapter's port settings are identical to what I'm using in PuTTY.

The only thing I get in the terminal window is a blank black screen, and a static green square marker.
For the record, in port settings > Advanced, I saw that "Use FIFO Buffers is checked". I tried switching that checkbox on and off, and restarting the device everytime I made a change, still same result.

I'm not really sure what am I doing wrong here or what's the cause of the problem. Please assist if you have any advice, this is starting to be hell of a pain in the neck.

Oh, and the router's completely inaccessible, too. I can't SSH\Telnet to it whatsoever. Can't do a thing, basically.

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