nothing is showing on the desktop, Finder won't open & Trash won't empty

Assuming your are running Lion 10.7, and not Leopard 10.5.8 such as your Profile shows, I would recommend that you reboot the computer while simultaneously holding down the Command - R keys to boot into the Lion Recovery Partition. Once there, open Disk Utility there and run "Disk Repair" on the hard drive, and then run "Repair Permissions" twice. Then restart and boot normally and see if your computer is working OK. If not, I think you'll need to return to the Lion Recovery Partition and run "Reinstall Lion", ASSUMING you have a good backup of your computer on an external hard drive that contains your uncorrupted data, apps, photos, music, etc. from a previous successful healthy backup. Then after reinstalling Lion, if you need to you can still use "Migration Assistant" to import those backed up personal files bask into your reinstalled Lion.

Hope this helps 🙂