Kevnash13 :
If I add 4Gb RAM to my excisting 4GB RAM, will there be a conflict if different brand?
The only potential conflict would lie in different speeds/timings of the different RAM. You should definitely match specs when purchasing. Do you know what RAM you have now?
It would be better to just buy a new 2x4GB kit, but if you can't afford it, it should work to just add more, again if you match specs will be the best.