My screen change the refresh rate auto?

My screen change the refresh rate automatically? Why?

Im using chaintech 6800nu

Sumtimes when do my work, the monitor suddenly like blank for 1 sec...

and when it on again i found out dat the monitor refresh rate set to default.

Is there sumthing wrong with my card? psu? monitor?

thanks...

this is my spec:

p4 [email protected]
256x2 value ram
p4p8x mobo
chaintech 6800 (61.77driver)
acbel 450w psu.

please help