Firstly I'd like to welcome you to the forums and say that I'm sorry to hear that your V+ box is giving you a hard time at the moment.
I've been able to locate your account, and have run some testing. I can see your V+ box is currently showing as offline, this may be down to the fault, or could be down to it being powered off.
Please let me know if your V+ box was powered on at the time of my post, if it wasn't, could you please power it back on and leave it powered on until we have gotten back to you after completing testing.
As nodrogd said, it may be that your output settings have changed in the box its self, so I'd suggest checking these out.
If they are still set to HDMI try changing some of the settings to different ratios, and if you still you can't view through HDMI, I'd ask you to try another HDMI cable also different HDMI ports on your TV. If you still then have the same issue, then I'd have to look towards getting a technician out, as it could be the HDMI port on the V+ box is faulty.