i was just about to click to see what you answer to your self, and i thought that you will write the above sentece. and you did.
you are the system administrator right? you have to know your system better than anything else in this world - this is your sole purpose. you have a problem - you have to resolve it. as prudent administrator you write down blueprint of your system - notes of hardware, os installation and configuration, 3rd party software, any bottle necks - os itselef, hardware and those made it by 3rd parties. what are you serving - heavy web pages or light web pages? flash? or html? is this system is hammered with requests for content? et cetera..et cetera.
and for the last - this is rude i know, dont thank me - one of my math lectors have a favourite answer to all my quiestions (i dont walk the math walk as i want to..): think before ask - this is what she says to me any time she see that i open my mouth. and she is right - 75% of the time i need minute or so to get the picture. you shoud try it
good luck