Imac Issues

Hey Guys,
i've got a 20'' Silver Imac. Lately i've noticed that some of my folders on the desk top have disappeared but the name is still there, if i d.click on the name the folder opens. Also my Iphoto will not open it gives me an error, an a sync error comes up when i plug in my Iphone, it all syncs properly though... Just a wee bit confused.... thanks for any feedback,
Bill

also

cannot change background pictures, i can look at the picture in preview. but it will not allow me to set as background picture. but i can use the factory mac ones...

I would run:

Disk Utility's Repair Permissions
OnyX
Disk Warrior (if you have it -- if you don't, buy it!)

Sounds like a storm brewing ...