LANPARTY UT nF4 Ultra-D Boot Problems

I have recently built a new system, but I am having problems getting to run properly. If you turn the power supply off and then switch it back on then power on the machine it will boot perfectly. However if you then restart the machine or power off the machine (not the power supply) it will fail to boot until you switch off the power supply.

The system spec is as shown below:-

AMD 64 3500+ (Winchester)
LANPARTY UT nF4 Ultra-D
XFX 6600GT PCI-E
74GB Western Digital Raptor
1GB Corsair Value Select
400W XCLIO Power Supply (as found at Scan)

I suspect it to be a problem with the power supply, but if you have any advice/suggestions I would greatly appreciate any help.

Cheers

Aaron