Computer doesn't shutdown!

[NizarBlond]

When I normally shut down/sleep mode , although the screen shuts down but the computer keeps running.

When I set the bios to "optimized default settings" it shuts down normally but the next time it doesn't.
Sometimes after a problematic shutdown it keeps restarting and having weird behavior. Once I got a warning asking me to stop over clocking, I never used it.

my spec is:

Video: AMD Radeon 6950 2GB
HD: Western Digital ‏Caviar Green 1TB IntelliPower, 64MB, SATA II WD10EARS‎
PS: ‏GS 700W Active PFC 14cm Fan
CPU: Intel i7 2700k 3.4Ghz Sandy Bridge
MB: ‏P67A-D3-B3 s1155 Core i3/i5/i7, Intel P67, DDR3 1333, 2xPCI-E‎

 

[M1kkelZR]

try to revert all settings back to default, turn OC off. or it could be that it cant actually cut power to the motherboard?

 

[NizarBlond]

what is OC? what settings? BIOS?
I don't get it please explain.

maybe I am afraid it is the power supply!
now for example when I turned the computer on, it kept restarting before reaching the windows starting. (it reaches the screen where I press DEL to get into BIOS, F12 Boot Menu and bla bla and then restarts)