black screen while overclocking

[b166erguy]

was looking at getting some extra performance so decided to overclock . . .
i have 8gb ddr3 1600 ram
fx 6300 3.5
and msi gtx 760 2gb

overclock on gpu
GPU CLOCK FROM 1020 TO 1150
MEMORY FROM 1502 TO 1680
BANDWITH FROM 192.3 TO 215.0

overclock on cpu
3.5 to 4.3

while i was trying to get to 4.4 i failed to boot n got a black screen with no way to access bios. removed the ram n powered on to beeped like mad so replaced the ram n no beeps at all reset cmos 1 beep (i always get 1 before full boot) but i still had black screen. decided the gpu wasnt talking to the tv so reset it in the board still to a black screen. by pure chance my friend phoned at this time n said he had a black screen while borrowing my pc and told me it had set to hdmi only so removed my vga and connected the tv via hdmi n sure enough my pc booted and displayed as normal just had to reset the clock as i had reset cmos. so what im wondering is how could changing cpu voltage and multiplier have caused the gpu to only display through hdmi instead of vga which i always use. i just dont get it. thanks alot for any ideas you have on this

 

[b166erguy]

Forgot to add while testing at 4.3 my stability was good passed all benchmarks windows assessment ect n occt for 40mins with voltage no more than 1.474 but my temp had rises to 50oC so thinking 4.3 is enough considering my cooler