I have a Power Tower/Z4/Apollo060 setup which recently had all sorts of boot problems.
I finally tied down the problem to the P8/P9 plugs supplying power to the Z4.
I suggest you thoroughly check the status of the connectors in the P8/P9 plugs.
They are very easily displaced/fatigued, which leads to all sorts of problems.
If you're handy at DIY, strip down the connectors and satisfy yourself that thay really are making good connections to the Z4. I've had no problems since.
Cheers,
JaX
