Nintendo 64 working for a few seconds then 'no signal'

Hi everyone! I recently bought a nintendo 64 and it has been working beautifully for the last 3 days but all of a sudden it has stopped working.

I have a new tv so I have an scart converter with power cord/hdmi linking it to the tv. The video and audio plays for a few seconds after I unplug/replug the hdmi cord then it returns to 'no signal'. The nintendo itself has its light on and seems to be working (as the game resumes to its positon no matter how many times I replug the hdmi).

The system is very clean too so I doubt that is the problem, any suggestions? The hdmi cord works when plugged in to separate consoles :(

Thank you in advance!!