Windows 7: Microphone doesn't work

A while ago i remember doing some configurations with my microphone to be able to record my guitar by just plugging it in, but i don't remember what i did, and it seems to have messed up my microphone. now, when i try to use skype, my microphone doesn't pick up my voice, saying that it "can't access my sound card". please help me out

what mic are you using - is it built in to the laptop..??

if it's an onboard mic, there should be a sound manager somewhere
that will allow you to enable it, and set recording levels, etc..

do you have a manual, that may give you some idea of where to look for the audio settings panel..??

it might also be worth checking the Dell site for sound drivers
re-installing them may reset the controls to "default", thus enabling the mic..

it's a built in microphone, and i've searched everywhere (at least i think) and i can't find it

it should be somewhere among these:
dell vostro 1700 driver download - P1 || Dell drivers || CD & Download Versions Available In ISO Format ||

make sure you get the right one..