Automatically starting up after I've shutdown (C-State Enabled/Disabled)

[zdexx]

Hi guys. I had a problem. Computer automatically starting up after I've shutdown. My system:
Windows 7
CPU - Intel Core i5-2400
MoBo - GIGABYTE GA-B75M-D3P
Memory - GoodRAM GY1600D364L9/8GDC
HDD - Western Digital Caviar Blue WD10EZEX 1TB
PSU - Chieftec Nitro BPS-550C
its workin with intel hd graphics.
With another chinese PSU i have no problem. I read a lot of solutions but nothing helped except one - its C3/C6 state support in the BIOS. This option was Enabled and i turn it to Disabled and it helped me. But with another PSU this option workin Is it safe to turn off the C-state? C1E Option still "Auto". Or I need change this PSU to another?
Thanks a lot.
But with this disabled option still reduced frequency to 1.6 GHz with no load.

 

[GhislainG]

If it works fine with another PSU, then the Chieftec Nitro BPS-550C has an issue.