my messy cable setup, can anyone give suggestion making it better?

My Room: setup
Samsung P2370MS (23") comes with all output same as lcd tv. HDMI, RCA, Component, DVID-D, Digital Audio out, VGA, built in speaker
Old Pc setup = Pentium D~ 1gb ram, Samsung dvd-burner, 120gb hdd, 1TB external hdd from samsung
PS3 Slim 120gb
20meter HDMI cable twin headed (one to the tv on the living room, another connecting to my lcd monitor inside my room), and hidden speakers

yup yup but weird la..this cable...i plug to my lcd monitor it cannot detect as 1080p, only 1080i (but my lcd tv outside can detect 1080p)
then then i tried those short cable belongs to my friend...able to detect 1080p on the same lcd monitor.. i wonder whats the problem