Can't change my wallpaper in Windows 7?

Yesterday i got a virus or something so i ran windows in safe mode and did a system restore to a couple days ago, the wallpaper i had was encrypted for some reason and now i can't use it so i found another wallpaper and tried to apply it but was told there was "an internal error" i've tried switching themes in the personalise window but the only wallpapers i can use are solid colours, any help???