My iPad will not sync or be recognized my iTunes anymore, help!!!

I have not changed anything on my PC and I'm using Windows Vista and I have synced my iPad2 with my PC a bunch of times but all of a sudden it's not recognizing my iPad anymore and won't sync it, it keeps telling me to restore my iPad. I can't restore because I have a drawing app that has over 400 sketches that I have sketched and if I don't back up my iPad before syncing it I will lose all of my sketches. If anyone has any tips, advice, or anyway to help me please let me know.

Thank you,

Darlene