what causing the black screens?

I bought a HIS ATI 4850, I read that u needs a 450W psu or higher, so i bought a 450w antec, I played CoD4 perfect in max settings with the gpu in default, but when i increase fan speed and core clock and memory i get a black screen or the monitor starts displaying retarded images. is it the psu that cant handle it or is the gpu messed up? the default on the gpu was core clock 625Mhz and 993 memory clock out of the box, then i i did auto tune from the CCC the card broght and it raised it to 690MHz core clock and like 1100 somrthing MHz memory clock.. then i get black screens and bad image when i play Cod4,so it freezes. is it my psu fault? and why is the memory clock so low if its advertised at 1986 MHz. Default was decent cause it was playing CoD 4 max settings 50-120fps, but in crysis it was in the 20-30s in high, i want this to do what it says. also my psu has almost no load, i only have 1 dvd drive, 1, HDD, and thats it.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814161235

I just knew this would be an ATI card. Not sure what is causing them. It sure isn't PSU or overheating in most cases but I had them a 1000 times on the X1950pro.

I know what you mean about the retarded image it is like all screwed up and colour bars etc.

the default on the gpu was core clock 625Mhz and 993 memory clock out of the box, then i i did auto tune from the CCC the card broght and it raised it to 690MHz core clock and like 1100 somrthing MHz memory clock.. then i get black screens and bad image when i play Cod4,so it freezes. and why is the memory clock so low if its advertised at 1986 MHz.

Raijinko

Maybe you are going too far with it.

ddr= double data rate.

1986= 993Mhz on your CCC you got to times those by 2. so 1100 is 2200Mhz

[QUOTE="Raijinko"]

the default on the gpu was core clock 625Mhz and 993 memory clock out of the box, then i i did auto tune from the CCC the card broght and it raised it to 690MHz core clock and like 1100 somrthing MHz memory clock.. then i get black screens and bad image when i play Cod4,so it freezes. and why is the memory clock so low if its advertised at 1986 MHz.

teddyrob

Maybe you are going too far with it.

ddr= double data rate.

1986= 993Mhz on your CCC you got to times those by 2. so 1100 is 2200Mhz