I recommend you uninstalling the current driver in your computer and download the latest one at the link:
Since it was working fine before and no changes have been made, I also recommend you to testing another HDMI cable since the problem can be related to the cable.
Besides the mentioned above, I recommend you doing a power cycle. This is done by disconnecting the battery and pressing and holding the power button for about 1 minute.
thanks for the reply.
I have uninstalled the driver and installed teh one you suggested. I have also done a power cycle. Still not working.
The HDMI cable is OK as when plugged into the DVD player rather than the PC, all is fine.
Is there anything else that you recommend trying?