Power problem GA-P35C and p182 case

[fitzy2003]

just installed most of my new computer,but when i turn off the computer it reboots staright away by its self everytime.i have to hold down the button when it shuts down then it reboots and then it turns off properly.

 

[fitzy2003]

this is my setup that i put together yesterday,when i shut the computer down in windows it shuts down for 5 secs and it reboots automaticaly.

Antec Case P182
Gigabyte GA_P35C_DS3R (Socket 775) PCI-Express DDR2 & DDR3 Motherboard
Intel Core 2 Duo E6750 "LGA775 Conroe" 2.66GHz (1333FSB) - Retail
GeIL 2GB (2x1GB) PC6400C4 800MHz Ultra Low Latency DDR2 Dual Channel Kit
Western Digital Caviar 400GB 7200RPM S300 16MB
Corsair Memory 520 Watt, ATX, EPS12V, PS/2, Modular Power Supply
Sapphire ATI Radeon HD 2900 Pro SILENT Heatpipe 512MB GDDR3 VIVO TV-Out/Dual DVI (PCI-Express)