I need help restoring my gateway

Hello,



i have no idea what i did to my computer but i did it so now I'm trying to get it back to its factory settings, i don't know much about computers and i got it from a friend and he didn't give me the recovery disk.

windows vista home premium
service pack 2
intel(R) core(TM)2 cpu t5200 @ 1.60 GHz

32-bit operating system

RAM 1.00 GB

please help