Need to reset computer to factory settings please help

Hello,
So I need help as to how to set my gateway with windows xp 2 factory settings. I have no disc it was given to kids... All the sites i've found told me to go to start all programs and gateway however this doesn't exist on my menu all it is is books that come up on how to use the darn computer. I tried alt and f10 it did nothing. Desperately seeking help its a fast computer however I cant see videos. It says I need adrob or something i tried to download it and no luck. So whatever was done to this i have no idea. I've never had a computer that doesn't have the adrobe already on it, or that u couldn't download it. It needs wiped back to the start... My kids cant get on pbs or the sites they like because it wont show n e videos. I apoligize about talking in circles, I tried to keep it simple but the problem isn't simple.. lol.. sorry and if you could help i'd really appriciate it.. Also itwont let me go to certian sites that could help me, keeps blocking them. I also cant download the most current norton or windows explorer thats how i ended up on firefox. thank you patty