display problems come back after reset the PRAM/VRAM

I have been having this display problem where in normal startup I get a black space where my desktop pic is, anything I run the cursor over turns black, clicking on the apple to turn off or log out only gets me color blocks. Everything boots up in safe mode, when I open a web page or a lrg e-mail the screen does this kinda of wave from top to bottom. I have already reset Pram/Vram, everything worked for a few hours then back to the same problem, I have updated, cleared out cache files, ran mackeeper, talked my way through another pram/vram with support only to have it happen soon after. We have ruled out hardware and are looking at software but other than going back to a blank mac what else can I try?

thanks for any help, if you need my support # from last time let me know.

Betty