Yaesu FT-450D not broken

I thought my FT-450D rig had developed a fault but I was wrong.
Essentially I was mid QSO with an Australian station both of us operating low power JT65A (I was transmitting 5 watts). I use HRD and JT65HF HB9HQX to control the rig. All of a sudden the PC started making beeping noises (the one when you unplug a USB device) and the rig was powering off and on by itself.

I disconnected everything and the rig would not power on. When I put the CAT cable back into the D9 on the back panel it powered up. However it would not TX and kept rebooting when I tried.
Thinking that it had developed a fault I emailed Yaesu customer service in the UK. A shortwhile later Sam Ruddy, the Yaesu Service manager, replied. One of the things he suggested was try the fuses in the power lead.

"Fuses?" I thought. "Are there two?"
Sure enough there are and the one in the negative lead had become loose in its holder. I don't know how but it had. Basically the rig had been powering on through the PC ground connection. When trying to TX the high current ground was going through the PC causing the rig to become disconnected from power and rebooting it. Fortunately there was no damage to either the rig nor the PC.

So when both fuses were reseated and everything reconnected all is working again. It just goes to show - get back to basics when you fault find.

Thanks to Sam Ruddy at Yaesu UK