I would recommend you contact me at the EMEA support office, as it may be that you need a repair/replacement on your HDLink.
If you please provide the above details, as well as the serial number of your HDLink unit and what video standards you are using with the HDLink (PAL, HD1080i50 etc), this will greatly assist the support team in identifying and solving your problem.
I hope to hear from you soon.
Technical Support Consultant
Blackmagic Design EMEA