Graphics card

Hi, I seem to be having probs with my graphics card. I have a dual monitor setup,but one of the monitors all off a sudden has changed resolution.
I am unable to set it to 1900x1280 like the other monitor. if I switch the cables over then it happens on the other monitor,so it is not the monitor but must be graphics card.
The card is ATI Radeon HD 4300/4500 Series.
If anyone has any suggestions on how to solve this problem,or if anyone could give me advice on a card I could buy that would do my job.
I am running Cubase on windows 64 bit. dual monitors. I don’t use pc for gaming.

Are you using the hdmi and dvi or two dvi ports? I am running 3 monitors out of my radeon 6700 but had to use 1 dvi 1 hdmi and the intel graphics port . When this happened to me it was all software driver related and was eventually resolved by deleting the driver …rebooting the computer and then re-installing the drivers for setup. The " identify monitors" button in control panel gave me a slight clue as to which was which when setting the resolution again. They do not seem to be recognized for what they are by windows but they did set up properly with a little tweaking