"Sound and Audio Devecies Properties"
Check both Advanced tabs and particulary the first on (volume tab). Ensure you click for recording properties the options for all greyed out/unticked devices like mic/line in etc. Also click the Advanced tab from drop down 'File' menu also - have a look at the dB booster option.
Check leads/ports at whichever socket you've using.
On reinterpreting your sentence, you have reinstalled windows XP operating system and now your soundcard (onboard or whatnot) is no longer available. Ah I see!!! Then ignore the above, and install the drivers for whichever device you have (there on one CD or other) or you can download fresh ones then do it that way. Just seems for some reason they're not installed this time round.
If sound isn't installed at all, not only the mic/line in etc won't function but neither will any sound be going out of your system - check the Device Manager (system properties and look for any yellow !exclamation marks! besides a device maybe...