Your blueray player is likely using HDCP. To attach the blueray player to your computer you would have to find a capture card that supports HDCP. To the best of my knowledge such a device does not exist.
It is my understanding that Monitors with HDMI ports are HDCP compliant. Therefore you can hook the blue-ray player up to the monitor. However as you mentioned you have the issue of sound. If the monitor has built-in speakers or audio out, you'll are good to go.
An Audio Converter such as the Orei DA21 (Optical SPDIF/Coaxial Digital to RCA L/R Analog Audio Converter) would allow you to convert the Digital Coaxial connection to RCA Analog. Note the Orei DA21 was the first device that appeared after a quick google search and is used simply for an example.
A brief description from Samsung on what HDCP is all about.
LCD: What Is High-Bandwidth Digital Content Protection System (HDCP)?
HDCP (High-Bandwidth Digital Content Protection) is a specification developed by Intel Corporation to protect digital content passed between DVI (Digital Video Interface) compliant video transmitters (computers, for example) and DVI compliant video receivers (monitors, televisions, etc.). In the past three years, the HDCP specification has been extended to HDMI compliant equipment such as TVs.
Before transmitting digital content, the transmitter transmits special HDCP device keys to the video receiver which only accepts content if it receives the correct keys. After the receiver has received the device keys, the transmitter and receiver generate another value that is transmitted and constantly checked as the digital content is transmitted to verify the transmission. To further protect the transmission, the transmitter encrypts the data before it sends it.