Mini displayport to hdmi problems on T430

[acore]

I have a T430. To show it on my TV I have bought a mini displayport to HDMI converter. The setup is T430->converter->5m HDMI cable->TV). It works, but after a while it stops working (no signal on TV, no change in resolution on PC).

I have tried in total 4 converters of 2 different makes (Lindy and Sandberg) - all with the same result. When a converter has stopped working, it is permanent.

This made me think that it could be a problem with the PC.

Does anyone have a view on what the problem might be or how to resolve it?