Those adapters can not work well with each other. We can try something if you want, but I don't think it will help.
If you feel like trying, first disable all unused ports in the bios like serial, parallel, floppy etc...
Right click on the 7500 in the device manager. Properties. Details tab. Change dropdown to hardware ids. Copy and paste the results here.
Also, tell me exactly which driver
you're currently using for the 4800. A link to it would be helpful. Extract that driver to C:\ATI and I can tell you what to do next, after you post.