Replacement Graphics Card Advice Wanted?.

Although my PC is quite old at 6yrs unfortunately at the present time I cannot afford to build a new one . My motherboard is http://uk.gigabyte.com/Motherboard/GA-MA770T-UD3-rev-14#ov and the Graphics Card installed is an AMD Radeon HD 5750. For some time now I have been bothered with 2-3 horizontal lines about an inch or so up from the bottom of my monitor which seems to only be triggered when I am browsing the internet. They do not appear when watching videos or playing games. I play Elite Dangerous a lot and it all plays perfectly smoothly with the Graphics running at 70 degrees max and no other problems. I have checked for the lines problem and applied the various Windows OS solutions including a new cable and checking against another monitor but to no avail. I read somewhere during these searches that it may also be a sign of the card beginning to fail. I have a new build in mind but that will be some months in the future before I can afford it, in the meantime if the card should fail I would like to know of a ready made replacement compatible for the above noted motherboard but am unsure of what I am looking for. Easiest would be a like for like replacement but it isn't sure I could find one which was unused?. I am an older gent at 67yrs and haven't got a problem putting parts together once I know what it is I need. Thanks for any help or advice offered.

Thanks for the reply but not sure that a used card is what I want. Chances are it will be a bit hit and miss at best, I would really like to know what type of card is compatible with my present motherboard and AMD Athlon II x3 450 CPU and see if I could find even a better/more expensive card that would work.

I suggest you to replace a amd 6870 used graphic card or 7000 series graphic card it is stiil good, for modern game, im using radeon hd 6870 but still can play watchdog with medium setting,