I have a T3600 with the 635w power supply.

Lately it's developed an issue where it won't boot properly. Behaviour is, press power button on front panel, relay in power supply clicks twice in rapid succession. Fans come on and some of the number lights near the front usb ports flash for about 3 seconds. Then the whole thing shuts down. Does this consistently.

The work around I discovered is to press the power supply test button at the back of the machine. The power supply then goes through it's test routine perfectly and shuts off.

Then if I press the front panel power button it boots up perfectly.

So, the power supply passes the test button test perfectly. I've disconnected and reconnected all the internal power cables and they seem fine.

Everything else seems to work fine.