For the icons, check, which icon theme is used! I don't remember where it is, but somewhere in the LXDE "Start" menu you should find an option to configure themes. Then, also check if the packages hicolor-icon-theme and lxde-icon-theme are installed! For the desktop wallpaper, check in pcmanfm's settings (the file manager) if it is set to "manage the desktop"! These are at least the reasons I've come across that would explain why your desktop looks the way it does. I find it odd though, that you have all three problems at once, so there might be a different reason.