in a spot of bother :| ... !?

OK.. so something happened to my pc, which made me think i should renew its lithium battery :| ... when i did so, it wouldnt reboot normally and to cut out unnecessary drivel.. i think i ended up performing a "reformat" on it ..or reloading windows xp pro ( never done that before.. :\ ) anyways ... i have a 9.41GB and a 3.01GBmy 9.41 being my c: drive ... and my 3.01 had all my personal settings etc.. ..So... When i finished doing what it told me to do...the drives have swapped with each other and ive gone from having approx 30% frees space on both drives to having 27% on one and 6% on the other... and all my stuff has been wiped :| .. how can that happen?? its taken my space and my stuff >.< .. pls assist if you can ?