When did that happen with yours, how old is it?
I don't know whether they are the same Mobo but I have been in contact with Humax as regards parts, this is what they came back with just now
Front Board - £21.65
Power Supply - £15.42
Main Board - Mainboards need to be programmed by Humax so not available to sell.
They quote £120 to repair but I mentioned that I have fitted Custom Firmware and they said they won't repair (thought best to mention it cos they would soon know if they got it working with the original mobo). And obviously I couldn't revert mine as its not working.
I have received, today, a 2 year old working one from eBay for £75 so I hope to work out what is wrong with mine and (unless its the mobo) will get them both operational.