I seem to have problems with my graphics card. Yesterday a couple of kids are playing my rig (which is oblivious to me because I'm asleep at that time). Then my brother called me and said that the display on our monitor has become color green. I thought it was just the setting on my monitor, but actually it was my dvi connector not properly plugged. I plugged it carefully again and it went back to normal. When I played NBA 2K13 with my friend, I noticed that the graphics suddenly become darker at times. I thought it was my settings, but in all of my games it happens as well. My games seem to run smoothly when I play but I get the occasional darkening of the in-game graphics and also when watching movies. What could be the problem and how to solve it? Do I have to just change my cable or the GPU itself? Thanks for the future responses fellow gamers. God bless you all. 
By the way my build is this
Intel Core i5-3470 (3.2G) 6mb 22nm
Asus P8H77-M LE H77 VSL
RipJaws 8gb 1600 (12800CL10S) 2*4
1.0TB Seagate Barracuda
EVGA GTX650 Ti SC 1gb ddr5 hdmi
Antec One
BENQ 21.5 GW2250BK (1920X1080) WIDESCREEN BLACK MONITOR
FSP Supersonic Series 80PLUS SLI 700w
Asus 24x 24B3/5ST sata

By the way my build is this
Intel Core i5-3470 (3.2G) 6mb 22nm
Asus P8H77-M LE H77 VSL
RipJaws 8gb 1600 (12800CL10S) 2*4
1.0TB Seagate Barracuda
EVGA GTX650 Ti SC 1gb ddr5 hdmi
Antec One
BENQ 21.5 GW2250BK (1920X1080) WIDESCREEN BLACK MONITOR
FSP Supersonic Series 80PLUS SLI 700w
Asus 24x 24B3/5ST sata