i build a PC recently, and eventually i need to RMA the mobo
maybe its not a matter, but do i need to clean up the thermal paste and apply new one ?
or i can just use the one i paste at first (the heatsink come with pasted thermal paste)
when i remove the heat sink and processor i put back at their plastic cap so the thermal paste remain untouched and didn't get dust
should i buy new thermal paste and re-apply again ?
If I were in your position, I personally would clean off the thermal paste and re-apply a new layer. I also tend not to use the thermal paste that comes pre-applied or with heatsinks anyways, as it can sometimes be of lower quality. I usually use Arctic Silver in my builds for my choice of thermal paste. There's probably other good ones out there, and you may be able to get away with reusing the paste you have, as long as you get 100% coverage between your CPU and heatsink with the thermal paste, but this is simply what I would have done.
Hi slyphnier, Any time that you remove your CPU heatsink you want to remove to old paste with a Q-tip or a cotton ball with a little isopropyl alcohol on it. Clean it very well so there is no left over paste, then re-apply new paste like Artic Silver 5 or OCZ Artic Freeze, only put a small rice grain size of paste in the center of the CPU then re-install your Heatsink.